# EDGAR Filing Document

**Accession Number:** 0000732337
**File Stem:** 0001133228-26-008620
**Filing Date:** 2026-6
**Character Count:** 184393
**Document Hash:** de537b8f5488df2854818f14e8d85526
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001133228-26-008620.hdr.sgml**: 20260601

**ACCESSION NUMBER**: 0001133228-26-008620

**CONFORMED SUBMISSION TYPE**: N-CSRS

**PUBLIC DOCUMENT COUNT**: 28

**CONFORMED PERIOD OF REPORT**: 20260331

**FILED AS OF DATE**: 20260601

**DATE AS OF CHANGE**: 20260601

**EFFECTIVENESS DATE**: 20260601

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** PUTNAM MORTGAGE SECURITIES FUND
- **CENTRAL INDEX KEY:** 0000732337

**ORGANIZATION NAME:**
- **EIN:** 042811119
- **STATE OF INCORPORATION:** MA
- **FISCAL YEAR END:** 0930

**FILING VALUES:**
- **FORM TYPE:** N-CSRS
- **SEC ACT:** 1940 Act
- **SEC FILE NUMBER:** 811-03897
- **FILM NUMBER:** 261049912

**BUSINESS ADDRESS:**
- **STREET 1:** 100 FEDERAL STREET
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02110
- **BUSINESS PHONE:** 6172921000

**MAIL ADDRESS:**
- **STREET 1:** 100 FEDERAL STREET
- **CITY:** BOSTON
- **STATE:** MA
- **ZIP:** 02110

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PUTNAM U S GOVERNMENT INCOME TRUST
- **DATE OF NAME CHANGE:** 19920703

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PUTNAM U S GOVERNMENT GUARANTEED SECURITIES INCOME TRUST
- **DATE OF NAME CHANGE:** 19910102

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PUTNAM UNITED STATES GOVERNMENT SECURITIES INCOME FUND
- **DATE OF NAME CHANGE:** 19840806

## Series and Classes Contracts Data

### PUTNAM MORTGAGE SECURITIES FUND (Series ID: S000006570)

| Class ID   | Class Name      | Ticker Symbol   |
|:---|:---|:---|
| C000017922 | Class A Shares  | PGSIX           |
| C000017924 | Class C Shares  | PGVCX           |
| C000017926 | Class R Shares  | PGVRX           |
| C000017927 | Class Y Shares  | PUSYX           |
| C000200295 | Class R6 Shares |  |

?xml version='1.0' encoding='ASCII'? 2026-04-2074200177600_PutnamMortgageSecuritiesFund_ClassA_TSRSemiAnnual

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

**FORM N-CSR**

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number **811-03897**

**Putnam Mortgage Securities Fund**

(Exact name of registrant as specified in charter)

**100 Federal Street, Boston, Massachusetts 02110**

(Address of principal executive offices) (Zip code)

Stephen Tate, Vice President

100 Federal Street

Boston, Massachusetts 02110

Copy to:

Bryan Chegwidden, Esq.

Ropes & Gray LLP

1211 Avenue of the Americas

New York, New York 10036

James E. Thomas, Esq.

Ropes & Gray LLP

800 Boylston Street

Boston, Massachusetts 02199

(Name and address of agent for service)

Registrant's telephone number, including area code: **(617) 292-1000**

Date of fiscal year end: **September 30**

Date of reporting period: **March 31, 2026**

ITEM 1. REPORT TO STOCKHOLDERS.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) The Report to Shareholders is filed herewith

---

| | |
|:---|:---|
| **Putnam Mortgage Securities Fund**  | ![image](img2199_202405220716489.jpg) |
| Class A [PGSIX] | ![image](img2199_202405220716489.jpg) |
| Semi-Annual Shareholder Report \| March 31, 2026  | ![image](img2199_202405220716489.jpg) |
| ![image](img2195_202408190904545.jpg) | ![image](img2195_202408190904545.jpg) |

---

This semi-annual shareholder report contains important information about Putnam Mortgage Securities Fund for the period October 1, 2025, to March 31, 2026.

You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.

**WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?** (based on a hypothetical $10,000 investment)

---

| | | |
|:---|:---|:---|
| **Class Name** | **Costs of a $10,000** **investment** | **Costs paid as a percentage of a** **$10,000 investment**<sup>†</sup>  |
| Class A | $45 | 0.88% |

---

† Annualized.

**KEY FUND STATISTICS** (as of March 31, 2026)

---

| | |
|:---|:---|
| **Total Net Assets** | $386100916 |
| **Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)** | 400 |
| **Portfolio Turnover Rate** | 435% |

---

**WHAT DID THE FUND INVEST IN?** (as of March 31, 2026)

**Portfolio Composition**<sup>\*</sup> **(% of Total Investments)**

![image](ts7092img003.jpg)

\* Does not include derivatives, except purchased options, if any.

---

| | |
|:---|:---|
| ![image](img11308_202405310907293.jpg) | **WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?** |
| ![image](img11308_202405310907293.jpg) | Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its: |
| ![image](img11308_202405310907293.jpg) | • prospectus • proxy voting information • financial information • holdings • tax information |

---

Putnam Mortgage Securities Fund PAGE 1 38913-STSA-0526

60.913.110.66.81.96.7 ------

---

| | |
|:---|:---|
| **Putnam Mortgage Securities Fund**  | ![image](img2199_202405220716489.jpg) |
| Class C [PGVCX] | ![image](img2199_202405220716489.jpg) |
| Semi-Annual Shareholder Report \| March 31, 2026  | ![image](img2199_202405220716489.jpg) |
| ![image](img2195_202408190904545.jpg) | ![image](img2195_202408190904545.jpg) |

---

This semi-annual shareholder report contains important information about Putnam Mortgage Securities Fund for the period October 1, 2025, to March 31, 2026.

You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.

**WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?** (based on a hypothetical $10,000 investment)

---

| | | |
|:---|:---|:---|
| **Class Name** | **Costs of a $10,000** **investment** | **Costs paid as a percentage of a** **$10,000 investment**<sup>†</sup>  |
| Class C | $83 | 1.63% |

---

† Annualized.

**KEY FUND STATISTICS** (as of March 31, 2026)

---

| | |
|:---|:---|
| **Total Net Assets** | $386100916 |
| **Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)** | 400 |
| **Portfolio Turnover Rate** | 435% |

---

**WHAT DID THE FUND INVEST IN?** (as of March 31, 2026)

**Portfolio Composition**<sup>\*</sup> **(% of Total Investments)**

![image](ts7097img003.jpg)

\* Does not include derivatives, except purchased options, if any.

---

| | |
|:---|:---|
| ![image](img11308_202405310907293.jpg) | **WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?** |
| ![image](img11308_202405310907293.jpg) | Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its: |
| ![image](img11308_202405310907293.jpg) | • prospectus • proxy voting information • financial information • holdings • tax information |

---

Putnam Mortgage Securities Fund PAGE 1 38913-STSC-0526

60.913.110.66.81.96.7 ------

---

| | |
|:---|:---|
| **Putnam Mortgage Securities Fund**  | ![image](img2199_202405220716489.jpg) |
| Class R [PGVRX] | ![image](img2199_202405220716489.jpg) |
| Semi-Annual Shareholder Report \| March 31, 2026  | ![image](img2199_202405220716489.jpg) |
| ![image](img2195_202408190904545.jpg) | ![image](img2195_202408190904545.jpg) |

---

This semi-annual shareholder report contains important information about Putnam Mortgage Securities Fund for the period October 1, 2025, to March 31, 2026.

You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.

**WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?** (based on a hypothetical $10,000 investment)

---

| | | |
|:---|:---|:---|
| **Class Name** | **Costs of a $10,000** **investment** | **Costs paid as a percentage of a** **$10,000 investment**<sup>†</sup>  |
| Class R | $57 | 1.13% |

---

† Annualized.

**KEY FUND STATISTICS** (as of March 31, 2026)

---

| | |
|:---|:---|
| **Total Net Assets** | $386100916 |
| **Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)** | 400 |
| **Portfolio Turnover Rate** | 435% |

---

**WHAT DID THE FUND INVEST IN?** (as of March 31, 2026)

**Portfolio Composition**<sup>\*</sup> **(% of Total Investments)**

![image](ts7099img003.jpg)

\* Does not include derivatives, except purchased options, if any.

---

| | |
|:---|:---|
| ![image](img11308_202405310907293.jpg) | **WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?** |
| ![image](img11308_202405310907293.jpg) | Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its: |
| ![image](img11308_202405310907293.jpg) | • prospectus • proxy voting information • financial information • holdings • tax information |

---

Putnam Mortgage Securities Fund PAGE 1 38913-STSR-0526

60.913.110.66.81.96.7 ------

---

| | |
|:---|:---|
| **Putnam Mortgage Securities Fund**  | ![image](img2199_202405220716489.jpg) |
| Class R6 [POLYX] | ![image](img2199_202405220716489.jpg) |
| Semi-Annual Shareholder Report \| March 31, 2026  | ![image](img2199_202405220716489.jpg) |
| ![image](img2195_202408190904545.jpg) | ![image](img2195_202408190904545.jpg) |

---

This semi-annual shareholder report contains important information about Putnam Mortgage Securities Fund for the period October 1, 2025, to March 31, 2026.

You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.

**WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?** (based on a hypothetical $10,000 investment)

---

| | | |
|:---|:---|:---|
| **Class Name** | **Costs of a $10,000** **investment** | **Costs paid as a percentage of a** **$10,000 investment**<sup>†</sup>  |
| Class R6 | $25 | 0.49% |

---

† Annualized.

**KEY FUND STATISTICS** (as of March 31, 2026)

---

| | |
|:---|:---|
| **Total Net Assets** | $386100916 |
| **Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)** | 400 |
| **Portfolio Turnover Rate** | 435% |

---

**WHAT DID THE FUND INVEST IN?** (as of March 31, 2026)

**Portfolio Composition**<sup>\*</sup> **(% of Total Investments)**

![image](ts7100img003.jpg)

\* Does not include derivatives, except purchased options, if any.

---

| | |
|:---|:---|
| ![image](img11308_202405310907293.jpg) | **WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?** |
| ![image](img11308_202405310907293.jpg) | Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its: |
| ![image](img11308_202405310907293.jpg) | • prospectus • proxy voting information • financial information • holdings • tax information |

---

Putnam Mortgage Securities Fund PAGE 1 38913-STSR6-0526

60.913.110.66.81.96.7 ------

---

| | |
|:---|:---|
| **Putnam Mortgage Securities Fund**  | ![image](img2199_202405220716489.jpg) |
| Class Y [PUSYX] | ![image](img2199_202405220716489.jpg) |
| Semi-Annual Shareholder Report \| March 31, 2026  | ![image](img2199_202405220716489.jpg) |
| ![image](img2195_202408190904545.jpg) | ![image](img2195_202408190904545.jpg) |

---

This semi-annual shareholder report contains important information about Putnam Mortgage Securities Fund for the period October 1, 2025, to March 31, 2026.

You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) 225-1581.

**WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS?** (based on a hypothetical $10,000 investment)

---

| | | |
|:---|:---|:---|
| **Class Name** | **Costs of a $10,000** **investment** | **Costs paid as a percentage of a** **$10,000 investment**<sup>†</sup>  |
| Class Y | $32 | 0.63% |

---

† Annualized.

**KEY FUND STATISTICS** (as of March 31, 2026)

---

| | |
|:---|:---|
| **Total Net Assets** | $386100916 |
| **Total Number of Portfolio Holdings (excludes derivatives, except purchased options, if any)** | 400 |
| **Portfolio Turnover Rate** | 435% |

---

**WHAT DID THE FUND INVEST IN?** (as of March 31, 2026)

**Portfolio Composition**<sup>\*</sup> **(% of Total Investments)**

![image](ts7102img003.jpg)

\* Does not include derivatives, except purchased options, if any.

---

| | |
|:---|:---|
| ![image](img11308_202405310907293.jpg) | **WHERE CAN I FIND ADDITIONAL INFORMATION ABOUT THE FUND?** |
| ![image](img11308_202405310907293.jpg) | Additional information is available on https://www.franklintempleton.com/regulatory-fund-documents, including its: |
| ![image](img11308_202405310907293.jpg) | • prospectus • proxy voting information • financial information • holdings • tax information |

---

Putnam Mortgage Securities Fund PAGE 1 38913-STSY-0526

60.913.110.66.81.96.7 ------

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b) Not applicable

ITEM 2. CODE OF ETHICS.

Not applicable.

ITEM 3. AUDIT COMMITTEE FINANCIAL EXPERT.

Not applicable.

ITEM 4. PRINCIPAL ACCOUNTANT FEES AND SERVICES.

Not applicable.

ITEM 5. AUDIT COMMITTEE OF LISTED REGISTRANTS.

Not applicable.

ITEM 6. SCHEDULE OF INVESTMENTS.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) Please see schedule of investments contained in the Financial Statements and Financial
 Highlights included under Item 7 of this Form N-CSR.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b) Not applicable.

ITEM 7. FINANCIAL STATEMENTS AND FINANCIAL HIGHLIGHTS FOR OPEN-END MANAGEMENT INVESTMENT COMPANIES.

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Financial

#### Statements

#### and

#### Other

#### Important

#### Information

#### Semi-Annual
\|

March 31, 2026

#### If

#### you

#### need

#### assistance

#### accessing

#### this

#### content,

#### please

#### reach

#### out

#### to

#### your

#### sales

#### representative

#### or

#### send

#### an

#### email

#### to

#### accessibility@franklintempleton.com

#### .

#### Table

#### of

#### Contents
franklintempleton.com

Financial

Statements

and

Other

Important

Information—Semiannual

Financial

Highlights

and

Schedule

of

Investments

#### 2
Financial

Statements

#### 21
Notes

to

Financial

Statements

#### 25
Changes

In

and

Disagreements

with

Accountants

#### 41
Results

of

Meeting(s)

of

Shareholders

Remuneration

Paid

to

Directors,

Officers

and

Others

Board

Approval

of

Management

and

Subadvisory

Agreements

Putnam

Mortgage

Securities

Fund

Financial

Highlights

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### 2024

#### 2023

#### 2022

#### 2021

#### Class

#### A

#### Per

#### share

#### operating

#### performance
(for

a

share

outstanding

throughout

the

period)

Net

asset

value,

beginning

of

period

.....

$7.88

$8.64

$8.34

$9.65

$11.87

$12.02

Income

from

investment

operations

a

:

Net

investment

income

b

.............

0.20 0.47 0.59 0.59 0.55 0.53 Net

realized

and

unrealized

gains

(losses)

0.08 (0.07)

0.58 (0.67)

(2.28)

(0.19)

Total

from

investment

operations

........

0.28 0.40 1.17 (0.08)

(1.73)

0.34 Less

distributions

from:

Net

investment

income

..............

(0.22)

(1.16)

(0.87)

(1.23)

(0.49)

(0.14)

Tax

return

of

capital

................

—

—

—

—

—

(0.35)

Total

distributions

...................

(0.22)

(1.16)

(0.87)

(1.23)

(0.49)

(0.49)

Net

asset

value,

end

of

period

..........

$7.94

$7.88

$8.64

$8.34

$9.65

$11.87

Total

return

c

.......................

3.63%

5.59%

14.76%

(1.41)%

(14.96)%

2.80%

#### Ratios

#### to

#### average

#### net

#### assets

#### d
Expenses

before

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.90%

0.92%

0.95%

0.97%

0.92%

0.89%

Expenses

net

of

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.88%

0.91%

0.95%

e

0.97%

e,f

0.92%

e,f,g

0.78%

e

Net

investment

income

...............

5.09%

5.93%

6.98%

6.52%

5.02%

4.29%

#### Supplemental

#### data
Net

assets,

end

of

period

(000's)

........

$345,984

$359,037

$391,226

$375,957

$442,394

$606,657

Portfolio

turnover

rate

................

435%

1013%

1383%

1500%

863%

974%

a

The

amount

shown

for

a

share

outstanding

throughout

the

period

may

not

correlate

with

the

Statement

of

Operations

for

the

period

due

to

the

timing

of

sales

and

repurchases

of

the

Fund's

shares

in

relation

to

income

earned

and/or

fluctuating

fair

value

of

the

investments

of

the

Fund.

b

Based

on

average

daily

shares

outstanding.

c

Total

return

does

not

reflect

sales

commissions

or

contingent

deferred

sales

charges,

if

applicable,

and

is

not

annualized

for

periods

less

than

one

year.

d

Ratios

are

annualized

for

periods

less

than

one

year.

e

Benefit

of

expense

reduction

rounds

to

less

than

0.01%.

f

Benefit

of

waiver

and

payments

by

affiliates

rounds

to

less

than

0.01%.

g

Includes

one-time

proxy

cost

of

0.01%.

Putnam

Mortgage

Securities

Fund

Financial

Highlights

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### 2024

#### 2023

#### 2022

#### 2021

#### Class

#### C

#### Per

#### share

#### operating

#### performance
(for

a

share

outstanding

throughout

the

period)

Net

asset

value,

beginning

of

period

.....

$7.77

$8.53

$8.24

$9.54

$11.74

$11.90

Income

from

investment

operations

a

:

Net

investment

income

b

.............

0.17 0.40 0.52 0.52 0.46 0.42 Net

realized

and

unrealized

gains

(losses)

0.07 (0.06)

0.58 (0.66)

(2.25)

(0.18)

Total

from

investment

operations

........

0.24 0.34 1.10 (0.14)

(1.79)

0.24 Less

distributions

from:

Net

investment

income

..............

(0.19)

(1.10)

(0.81)

(1.16)

(0.41)

(0.11)

Tax

return

of

capital

................

—

—

—

—

—

(0.29)

Total

distributions

...................

(0.19)

(1.10)

(0.81)

(1.16)

(0.41)

(0.40)

Net

asset

value,

end

of

period

..........

$7.82

$7.77

$8.53

$8.24

$9.54

$11.74

Total

return

c

.......................

3.17%

4.86%

13.94%

(2.07)%

(15.60)%

1.94%

#### Ratios

#### to

#### average

#### net

#### assets

#### d
Expenses

before

waiver

and

payments

by

affiliates

and

expense

reduction

........

1.65%

1.67%

1.70%

1.72%

1.67%

1.64%

Expenses

net

of

waiver

and

payments

by

affiliates

and

expense

reduction

........

1.63%

1.66%

1.70%

e

1.72%

e,f

1.67%

e,f,g

1.53%

e

Net

investment

income

...............

4.33%

5.17%

6.21%

5.76%

4.25%

3.44%

#### Supplemental

#### data
Net

assets,

end

of

period

(000's)

........

$1,536

$1,651

$1,613

$2,268

$3,467

$5,938

Portfolio

turnover

rate

................

435%

1013%

1383%

1500%

863%

974%

a

The

amount

shown

for

a

share

outstanding

throughout

the

period

may

not

correlate

with

the

Statement

of

Operations

for

the

period

due

to

the

timing

of

sales

and

repurchases

of

the

Fund's

shares

in

relation

to

income

earned

and/or

fluctuating

fair

value

of

the

investments

of

the

Fund.

b

Based

on

average

daily

shares

outstanding.

c

Total

return

does

not

reflect

sales

commissions

or

contingent

deferred

sales

charges,

if

applicable,

and

is

not

annualized

for

periods

less

than

one

year.

d

Ratios

are

annualized

for

periods

less

than

one

year.

e

Benefit

of

expense

reduction

rounds

to

less

than

0.01%.

f

Benefit

of

waiver

and

payments

by

affiliates

rounds

to

less

than

0.01%.

g

Includes

one-time

proxy

cost

of

0.01%.

Putnam

Mortgage

Securities

Fund

Financial

Highlights

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### 2024

#### 2023

#### 2022

#### 2021

#### Class

#### R

#### Per

#### share

#### operating

#### performance
(for

a

share

outstanding

throughout

the

period)

Net

asset

value,

beginning

of

period

.....

$7.74

$8.50

$8.22

$9.52

$11.71

$11.88

Income

from

investment

operations

a

:

Net

investment

income

b

.............

0.19 0.44 0.56 0.56 0.52 0.49 Net

realized

and

unrealized

gains

(losses)

0.07 (0.06)

0.57 (0.66)

(2.24)

(0.20)

Total

from

investment

operations

........

0.26 0.38 1.13 (0.10)

(1.72)

0.29 Less

distributions

from:

Net

investment

income

..............

(0.21)

(1.14)

(0.85)

(1.20)

(0.47)

(0.13)

Tax

return

of

capital

................

—

—

—

—

—

(0.33)

Total

distributions

...................

(0.21)

(1.14)

(0.85)

(1.20)

(0.47)

(0.46)

Net

asset

value,

end

of

period

..........

$7.79

$7.74

$8.50

$8.22

$9.52

$11.71

Total

return

c

.......................

3.45%

5.41%

14.41%

(1.58)%

(15.11)%

2.41%

#### Ratios

#### to

#### average

#### net

#### assets

#### d
Expenses

before

waiver

and

payments

by

affiliates

and

expense

reduction

........

1.15%

1.17%

1.20%

1.22%

1.17%

1.14%

Expenses

net

of

waiver

and

payments

by

affiliates

and

expense

reduction

........

1.13%

1.16%

1.20%

e

1.22%

e,f

1.17%

e,f,g

1.03%

e

Net

investment

income

...............

4.84%

5.68%

6.71%

6.27%

4.77%

4.02%

#### Supplemental

#### data
Net

assets,

end

of

period

(000's)

........

$3,290

$3,288

$4,151

$4,518

$4,593

$6,479

Portfolio

turnover

rate

................

435%

1013%

1383%

1500%

863%

974%

a

The

amount

shown

for

a

share

outstanding

throughout

the

period

may

not

correlate

with

the

Statement

of

Operations

for

the

period

due

to

the

timing

of

sales

and

repurchases

of

the

Fund's

shares

in

relation

to

income

earned

and/or

fluctuating

fair

value

of

the

investments

of

the

Fund.

b

Based

on

average

daily

shares

outstanding.

c

Total

return

is

not

annualized

for

periods

less

than

one

year.

d

Ratios

are

annualized

for

periods

less

than

one

year.

e

Benefit

of

expense

reduction

rounds

to

less

than

0.01%.

f

Benefit

of

waiver

and

payments

by

affiliates

rounds

to

less

than

0.01%.

g

Includes

one-time

proxy

cost

of

0.01%.

Putnam

Mortgage

Securities

Fund

Financial

Highlights

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### 2024

#### 2023

#### 2022

#### 2021

#### Class

#### R6

#### Per

#### share

#### operating

#### performance
(for

a

share

outstanding

throughout

the

period)

Net

asset

value,

beginning

of

period

.....

$7.73

$8.49

$8.21

$9.52

$11.71

$11.88

Income

from

investment

operations

a

:

Net

investment

income

b

.............

0.21 0.49 0.61 0.62 0.59 0.57 Net

realized

and

unrealized

gains

(losses)

0.08 (0.06)

0.58 (0.67)

(2.25)

(0.20)

Total

from

investment

operations

........

0.29 0.43 1.19 (0.05)

(1.66)

0.37 Less

distributions

from:

Net

investment

income

..............

(0.24)

(1.19)

(0.91)

(1.26)

(0.53)

(0.15)

Tax

return

of

capital

................

—

—

—

—

—

(0.39)

Total

distributions

...................

(0.24)

(1.19)

(0.91)

(1.26)

(0.53)

(0.54)

Net

asset

value,

end

of

period

..........

$7.78

$7.73

$8.49

$8.21

$9.52

$11.71

Total

return

c

.......................

3.79%

6.15%

15.25%

(1.04)%

(14.58)%

3.07%

#### Ratios

#### to

#### average

#### net

#### assets

#### d
Expenses

before

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.51%

0.51%

0.54%

0.56%

0.53%

0.52%

Expenses

net

of

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.49%

0.51%

e

0.54%

e

0.56%

e,f

0.53%

e,f,g

0.41%

e

Net

investment

income

...............

5.48%

6.33%

7.33%

6.94%

5.40%

4.67%

#### Supplemental

#### data
Net

assets,

end

of

period

(000's)

........

$3,508

$3,383

$3,979

$5,451

$5,123

$6,069

Portfolio

turnover

rate

................

435%

1013%

1383%

1500%

863%

974%

a

The

amount

shown

for

a

share

outstanding

throughout

the

period

may

not

correlate

with

the

Statement

of

Operations

for

the

period

due

to

the

timing

of

sales

and

repurchases

of

the

Fund's

shares

in

relation

to

income

earned

and/or

fluctuating

fair

value

of

the

investments

of

the

Fund.

b

Based

on

average

daily

shares

outstanding.

c

Total

return

is

not

annualized

for

periods

less

than

one

year.

d

Ratios

are

annualized

for

periods

less

than

one

year.

e

Benefit

of

expense

reduction

rounds

to

less

than

0.01%.

f

Benefit

of

waiver

and

payments

by

affiliates

rounds

to

less

than

0.01%.

g

Includes

one-time

proxy

cost

of

0.01%.

Putnam

Mortgage

Securities

Fund

Financial

Highlights

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### 2024

#### 2023

#### 2022

#### 2021

#### Class

#### Y

#### Per

#### share

#### operating

#### performance
(for

a

share

outstanding

throughout

the

period)

Net

asset

value,

beginning

of

period

.....

$7.72

$8.49

$8.21

$9.52

$11.71

$11.88

Income

from

investment

operations

a

:

Net

investment

income

b

.............

0.21 0.48 0.61 0.60 0.58 0.55 Net

realized

and

unrealized

gains

(losses)

0.07 (0.07)

0.57 (0.66)

(2.25)

(0.19)

Total

from

investment

operations

........

0.28 0.41 1.18 (0.06)

(1.67)

0.36 Less

distributions

from:

Net

investment

income

..............

(0.23)

(1.18)

(0.90)

(1.25)

(0.52)

(0.15)

Tax

return

of

capital

................

—

—

—

—

—

(0.38)

Total

distributions

...................

(0.23)

(1.18)

(0.90)

(1.25)

(0.52)

(0.53)

Net

asset

value,

end

of

period

..........

$7.77

$7.72

$8.49

$8.21

$9.52

$11.71

Total

return

c

.......................

3.71%

5.85%

15.08%

(1.17)%

(14.71)%

2.93%

#### Ratios

#### to

#### average

#### net

#### assets

#### d
Expenses

before

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.65%

0.67%

0.70%

0.72%

0.67%

0.64%

Expenses

net

of

waiver

and

payments

by

affiliates

and

expense

reduction

........

0.63%

0.66%

0.70%

e

0.72%

e,f

0.67%

e,f,g

0.53%

e

Net

investment

income

...............

5.32%

6.17%

7.24%

6.77%

5.23%

4.59%

#### Supplemental

#### data
Net

assets,

end

of

period

(000's)

........

$31,784

$40,676

$33,222

$22,575

$27,715

$77,518

Portfolio

turnover

rate

................

435%

1013%

1383%

1500%

863%

974%

a

The

amount

shown

for

a

share

outstanding

throughout

the

period

may

not

correlate

with

the

Statement

of

Operations

for

the

period

due

to

the

timing

of

sales

and

repurchases

of

the

Fund's

shares

in

relation

to

income

earned

and/or

fluctuating

fair

value

of

the

investments

of

the

Fund.

b

Based

on

average

daily

shares

outstanding.

c

Total

return

is

not

annualized

for

periods

less

than

one

year.

d

Ratios

are

annualized

for

periods

less

than

one

year.

e

Benefit

of

expense

reduction

rounds

to

less

than

0.01%.

f

Benefit

of

waiver

and

payments

by

affiliates

rounds

to

less

than

0.01%.

g

Includes

one-time

proxy

cost

of

0.01%.

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited),

March

31,

2026

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Asset-Backed

#### Securities

#### 4.8%

#### Financial

#### Services

#### 4.8%
Bayview

Financial

Mortgage

Pass-Through

Trust

,

2006-C

,

1A3

,

6.528 %

,

11/28/36

...

$

1,210,106

$

1,203,710

a

Bayview

Opportunity

Master

Fund

VII

Trust

,

2023-1A

,

A

,

144A,

6.93 %

,

10/28/60

....

239,021

244,680

b

Carrington

Mortgage

Loan

Trust

,

2006-NC2

,

A4

,

FRN

,

4.273 %

,

(1-month

SOFR

+

0.594 %),

6/25/36

..................................................

1,689,227

1,654,849

a

Castlelake

Aircraft

Structured

Trust

,

2025-2A

,

A

,

144A,

5.465 %

,

8/15/50

..........

800,871

801,841

b

CWABS,

Inc.

Asset-Backed

Certificates

Trust

,

2007-10

,

1A1

,

FRN

,

3.973 %

,

(1-month

SOFR

+

0.294 %),

6/25/47

...........................................

2,498,943

2,410,010

a

DataBank

Issuer

II

LLC

,

2025-1A

,

A2

,

144A,

5.18 %

,

9/27/55

...................

420,000

408,236

a

GGAM

Master

Trust

International

Ltd.

,

2025-1A

,

A

,

144A,

5.923 %

,

9/30/60

........

743,024

742,708

a

HTAP

Trust

,

2024-1

,

A

,

144A,

%

,

4/25/37

................................

998,870

1,000,537

a

MAST

Ltd.

,

2026-1A

,

A

,

144A,

5.134 %

,

2/15/51

.............................

1,482,125

1,459,969

b

Morgan

Stanley

ABS

Capital

I,

Inc.

Trust

,

2004-HE9

,

M2

,

FRN

,

4.723 %

,

(1-month

SOFR

+

1.044 %),

11/25/34

..........................................

11,866

11,893

a

New

Economy

Assets

-

Phase

Sponsor

LLC

,

2021-1

,

A1

,

144A,

1.91 %

,

10/20/61

..

1,026,000

863,226

a

PK

Alift

Loan

Funding

LP

,

2025-2

,

A

,

144A,

4.75 %

,

3/15/43

...................

235,871

235,052

a

PRET

LLC

,

2025-NPL9,

A1,

144A,

5.391%,

8/25/55

.................................

1,789,177

1,792,078

2026-NPL3,

A1,

144A,

4.968%,

2/25/56

.................................

1,478,644

1,467,631

a,b

PRMI

Securitization

Trust

,

2024-CMG1

,

A1

,

144A,

FRN

,

5.119 %

,

(30-day

SOFR

Average

+

1.45 %),

7/25/54

...........................................

568,744

568,257

a

Sabey

Data

Center

Issuer

LLC

,

2026-1

,

A2

,

144A,

5.482 %

,

1/20/51

..............

731,000

726,632

a

SF

ABS

Issuer

LLC

,

2025-1A

,

A2

,

144A,

5.377 %

,

11/25/55

....................

991,000

971,758

a,b

Towd

Point

Mortgage

Trust

,

2025-HE1

,

A1A

,

144A,

FRN

,

5.012 %

,

(30-day

SOFR

Average

+

1.35 %),

7/25/65

...........................................

823,827

824,261

a,c

Tricolor

Auto

Securitization

Trust

,

2024-1A,

A,

144A,

6.61%,

10/15/27

....................................

456,614

453,600

2025-1A,

A,

144A,

4.94%,

2/15/29

.....................................

266,833

165,010

a

VCAT

LLC

,

2026-NPL1

,

A1

,

144A,

5.101 %

,

1/25/56

..........................

222,591

221,513

b

Wells

Fargo

Home

Equity

Asset-Backed

Securities

Trust

,

2007-2

,

A3

,

FRN

,

4.253 %

,

(1-month

SOFR

+

0.574 %),

4/25/37

....................................

277,551

275,696

18,503,147

a

a

a

a

a

#### Total

#### Asset-Backed

#### Securities

#### (Cost

#### $18,333,854)

#### ...............................

#### 18,503,147

#### Commercial

#### Mortgage-Backed

#### Securities

#### 26.3%

#### Financial

#### Services

#### 26.3%
BANK

,

a

2018-BN11,

D,

144A,

3%,

3/15/61

.....................................

959,000

811,866

d,e

2024-BNK48,

XA,

IO,

FRN,

1.144%,

10/15/57

............................

9,561,238

737,945

d,e

BANK5

Trust

,

2024-5YR10

,

XA

,

IO,

FRN

,

1.188 %

,

10/15/57

...................

14,866,835

536,141

a

Barclays

Commercial

Mortgage

Trust

,

2019-C4,

E,

144A,

3.25%,

8/15/52

.....................................

2,034,000

1,146,668

e

2019-C5,

F,

144A,

FRN,

2.552%,

11/15/52

...............................

1,001,000

628,267

BBCMS

Mortgage

Trust

,

a

2026-5C40,

E,

144A,

4.25%,

2/15/59

...................................

1,000,000

695,057

d,e

2024-5C29,

XA,

IO,

FRN,

1.598%,

9/15/57

...............................

19,212,761

914,745

d,e

2025-C32,

XA,

IO,

FRN,

1.128%,

2/15/62

................................

10,550,305

847,022

a,d,e

2026-5C40,

XE,

IO,

144A,

FRN,

2.126%,

2/15/59

..........................

1,000,000

88,970

Benchmark

Mortgage

Trust

,

e

2018-B1,

C,

FRN,

4.202%,

1/15/51

....................................

718,000

589,759

a

2018-B1,

D,

144A,

2.75%,

1/15/51

.....................................

1,800,000

708,094

a,e

2018-B3,

D,

144A,

FRN,

3.045%,

4/10/51

...............................

1,141,000

800,118

a

2019-B11,

D,

144A,

3%,

5/15/52

......................................

1,556,000

878,113

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

Benchmark

Mortgage

Trust,

(continued)

a,e

2018-B1,

E,

144A,

FRN,

3%,

1/15/51

...................................

$

1,840,000

$

593,742

d,e

2024-V10,

XA,

IO,

FRN

,

1.305%,

9/15/57

................................

12,777,639

497,970

d,e

2024-V11,

XA,

IO,

FRN,

0.56%,

11/15/57

................................

23,287,961

433,394

d,e

2019-B15,

XA,

IO,

FRN,

0.8%,

12/15/72

.................................

13,430,696

307,474

d,e

BMO

Mortgage

Trust

,

2024-5C6

,

XA

,

IO,

FRN

,

1.353 %

,

9/15/57

................

11,391,980

443,000

a,e

BWAY

Mortgage

Trust

,

2022-26BW,

E,

144A,

FRN,

4.866%,

2/10/44

.............................

1,133,000

631,405

2022-26BW,

F,

144A,

FRN,

4.866%,

2/10/44

.............................

2,305,000

1,143,063

a,e

BX

Trust

,

2025-ARIA

,

C

,

144A,

FRN

,

5.517 %

,

12/13/42

.......................

773,000

771,512

CD

Mortgage

Trust

,

e

2017-CD3,

B,

FRN,

3.984%,

2/10/50

...................................

826,000

555,266

e

2017-CD4,

B,

FRN,

3.947%,

5/10/50

...................................

1,408,000

1,291,540

e

2017-CD3,

C,

FRN,

4.557%,

2/10/50

...................................

1,638,000

609,558

a

2017-CD3,

D,

144A,

3.25%,

2/10/50

....................................

1,567,128

94,459

a

2019-CD8,

D,

144A,

3%,

8/15/57

......................................

1,450,000

959,227

CFCRE

Commercial

Mortgage

Trust

,

2016-C7,

A3,

3.839%,

12/10/54

.......................................

624,000

620,344

a,e

2011-C2,

E,

144A,

FRN,

5.249%,

12/15/47

...............................

603,000

570,537

Citigroup

Commercial

Mortgage

Trust

,

e

2015-GC33,

C,

FRN,

4.336%,

9/10/58

..................................

770,000

671,247

a,e

2015-GC27,

D,

144A,

FRN,

4.379%,

2/10/48

.............................

1,517,660

1,485,765

2015-GC33,

D,

3.172%,

9/10/58

.......................................

250,000

153,750

a

2015-GC27,

E,

144A,

3%,

2/10/48

.....................................

2,035,000

1,900,608

COMM

Mortgage

Trust

,

2012-CR4,

AM,

3.251%,

10/15/45

.....................................

1,721,000

1,670,968

2013-CR12,

AM,

4.3%,

10/10/46

......................................

963,311

924,036

e

2014-UBS5,

AM,

FRN,

4.193%,

9/10/47

.................................

364,833

360,228

a

2012-CR4,

B,

144A,

3.703%,

10/15/45

..................................

924,000

629,099

2014-CR17,

B,

4.377%,

5/10/47

.......................................

615,153

609,494

e

2015-DC1,

B,

FRN,

4.035%,

2/10/48

...................................

1,285,000

1,232,572

a,e

2013-CR6,

C,

144A,

FRN,

3.777%,

3/10/46

..............................

765,000

745,157

e

2014-CR16,

C,

FRN,

4.724%,

4/10/47

..................................

1,741,904

1,673,722

e

2014-CR17,

C,

FRN,

4.471%,

5/10/47

..................................

1,360,000

1,285,497

e

2014-UBS3,

C,

FRN,

4.494%,

6/10/47

..................................

409,000

381,710

e

2014-UBS4,

C,

FRN,

4.457%,

8/10/47

..................................

397,060

314,075

a,e

2012-LC4,

D,

144A,

FRN,

5.351%,

12/10/44

.............................

2,249,245

1,733,532

a,e

2013-CR7,

D,

144A,

FRN,

4.152%,

3/10/46

..............................

677,929

664,751

a,e

2013-LC13,

D,

144A,

FRN,

5.012%,

8/10/46

.............................

2,439,484

2,290,861

a,e

2013-CR13,

D,

144A,

FRN,

6.702%,

11/10/46

............................

1,509,790

854,904

a,e

2014-CR17,

D,

144A,

FRN,

4.535%,

5/10/47

.............................

1,959,000

1,662,256

a,e

2014-UBS4,

D,

144A,

FRN,

4.52%,

8/10/47

..............................

757,000

178,865

a

2015-LC19,

D,

144A,

2.867%,

2/10/48

..................................

1,240,000

1,167,513

e

2015-CR26,

D,

FRN,

3.613%,

10/10/48

.................................

1,351,375

1,105,051

a

2017-COR2,

D,

144A,

3%,

9/10/50

.....................................

882,000

801,787

a,e

2018-COR3,

D,

144A,

FRN,

2.769%,

5/10/51

.............................

499,000

198,253

a

2013-LC6,

E,

144A,

3.5%,

1/10/46

.....................................

701,000

660,883

a,e

2015-LC19,

E,

144A,

FRN,

4.408%,

2/10/48

..............................

1,436,000

1,327,554

CSAIL

Commercial

Mortgage

Trust

,

e

2015-C1,

B,

FRN,

3.742%,

4/15/50

....................................

773,687

746,201

e

2015-C3,

C,

FRN,

4.13%,

8/15/48

.....................................

841,462

816,902

e

2015-C1,

C,

FRN,

3.742%,

4/15/50

....................................

644,000

602,285

e

2015-C2,

C,

FRN,

4.12%,

6/15/57

.....................................

299,852

287,440

a

2019-C17,

D,

144A,

2.5%,

9/15/52

.....................................

798,000

446,675

e

2015-C2,

D,

FRN,

4.12%,

6/15/57

.....................................

838,000

740,940

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

a,e

DBUBS

Mortgage

Trust

,

2011-LC3A

,

D

,

144A,

FRN

,

5.294 %

,

8/10/44

............

$

1,237,891

$

1,210,776

e

GS

Mortgage

Securities

Trust

,

2014-GC24,

B,

FRN,

4.297%,

9/10/47

..................................

646,251

625,807

a

2014-GC24,

D,

144A,

FRN,

4.318%,

9/10/47

.............................

1,892,000

1,314,921

a

2017-GS5,

D,

144A,

FRN,

3.509%,

3/10/50

..............................

1,021,000

107,708

J.P.

Morgan

Chase

Commercial

Mortgage

Securities

Trust

,

2013-LC11,

B,

3.499%,

4/15/46

.......................................

52,366

51,092

e

2013-C10,

C,

FRN,

3.905%,

12/15/47

..................................

336,733

326,885

a,e

2011-C3,

D,

144A,

FRN,

5.526%,

2/15/46

...............................

1,123,000

1,062,839

e

2013-LC11,

D,

FRN,

3.607%,

4/15/46

...................................

199,266

1,494

a,e

2012-LC9,

D,

144A,

FRN,

3.499%,

12/15/47

.............................

1,408,000

1,375,388

e

JPMBB

Commercial

Mortgage

Securities

Trust

,

2014-C18,

B,

FRN,

4.474%,

2/15/47

...................................

630,923

627,112

2014-C25,

B,

FRN,

4.347%,

11/15/47

...................................

1,497,000

1,398,529

2014-C22,

C,

FRN,

4.514%,

9/15/47

...................................

1,124,000

1,072,135

2013-C12,

D,

FRN,

3.859%,

7/15/45

...................................

1,408,000

1,340,306

a

2013-C14,

D,

144A,

FRN,

3.931%,

8/15/46

..............................

1,732,000

1,386,548

a

2014-C23,

D,

144A,

FRN,

4.037%,

9/15/47

..............................

726,000

665,949

a

2013-C12,

E,

144A,

FRN,

3.859%,

7/15/45

...............................

1,235,000

864,500

a,e

JPMCC

Commercial

Mortgage

Securities

Trust

,

2017-JP7

,

D

,

144A,

FRN

,

4.414 %

,

9/15/50

.........................................................

859,000

626,600

JPMDB

Commercial

Mortgage

Securities

Trust

,

2018-C8,

B,

4.522%,

6/15/51

.........................................

636,000

607,340

e

2018-C8,

C,

FRN,

4.755%,

6/15/51

....................................

835,000

767,412

a,e

2016-C2,

D,

144A,

FRN,

3.427%,

6/15/49

...............................

2,330,000

1,142,535

a

LSTAR

Commercial

Mortgage

Trust

,

2017-5

,

A5

,

144A,

3.549 %

,

3/10/50

..........

796,000

788,757

a,e

MAD

Commercial

Mortgage

Trust

,

2025-11MD

,

D

,

144A,

FRN

,

5.935 %

,

10/15/42

...

1,551,000

1,577,561

Morgan

Stanley

Bank

of

America

Merrill

Lynch

Trust

,

e

2013-C9,

B,

FRN,

3.708%,

5/15/46

....................................

958,842

915,907

e

2013-C10,

B,

FRN,

3.951%,

7/15/46

...................................

1,075,699

1,022,651

e

2013-C9,

C,

FRN,

3.704%,

5/15/46

....................................

1,398,000

1,291,667

e

2015-C22,

C,

FRN,

3.97%,

4/15/48

....................................

1,616,000

1,412,571

e

2017-C34,

C,

FRN

,

4.164%,

11/15/52

...................................

751,000

668,685

a,e

2013-C9,

D,

144A,

FRN,

3.792%,

5/15/46

...............................

1,122,000

1,026,282

a,e

2013-C12,

D,

144A,

FRN,

4.601%,

10/15/46

.............................

800,000

765,410

a

2014-C19,

D,

144A,

3.25%,

12/15/47

...................................

688,475

678,537

a,e

2012-C6,

E,

144A,

FRN,

4.345%,

11/15/45

...............................

1,677,000

1,146,666

a,e

2013-C12,

E,

144A,

FRN,

4.601%,

10/15/46

..............................

1,232,618

963,982

a,e

2013-C10,

F,

144A,

FRN,

3.951%,

7/15/46

...............................

2,316,000

355,197

a,e

2012-C6,

G,

144A,

FRN,

4.5%,

11/15/45

................................

1,288,000

73,652

e

Morgan

Stanley

Capital

I

Trust

,

2016-UB11,

C,

FRN,

3.691%,

8/15/49

..................................

1,920,000

1,895,956

a

2011-C3,

E,

144A,

FRN,

4.941%,

7/15/49

................................

1,306,711

1,295,104

a

PRET

LLC

,

2025-NPL4

,

A1

,

144A,

6.368 %

,

4/25/55

.........................

1,056,489

1,058,273

e

UBS

Commercial

Mortgage

Trust

,

2017-C3,

C,

FRN,

4.352%,

8/15/50

....................................

1,405,000

1,326,272

2018-C11,

C,

FRN,

4.867%,

6/15/51

...................................

986,000

916,221

a

2018-C11,

D,

144A,

FRN,

3%,

6/15/51

..................................

1,695,000

1,133,568

a

2012-C1,

E,

144A,

FRN,

5%,

5/10/45

...................................

1,132,786

1,080,372

a,e

VEGAS

,

2024-GCS

,

D

,

144A,

FRN

,

6.217 %

,

7/10/36

.........................

627,000

625,001

Wells

Fargo

Commercial

Mortgage

Trust

,

e

2015-C31,

C,

FRN,

4.672%,

11/15/48

...................................

16,430

16,191

e

2016-BNK1,

C,

FRN,

3.071%,

8/15/49

..................................

790,000

572,421

e

2018-C46,

C,

FRN,

4.947%,

8/15/51

...................................

868,000

816,998

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

Wells

Fargo

Commercial

Mortgage

Trust,

(continued)

e

2020-C57,

C,

FRN,

4.023%,

8/15/53

...................................

$

418,000

$

382,516

e

2015-C29,

D,

FRN,

4.091%,

6/15/48

...................................

116,788

113,583

2015-C31,

D,

3.852%,

11/15/48

.......................................

2,189,000

1,986,124

a

2017-RB1,

D,

144A,

3.401%,

3/15/50

...................................

991,000

451,493

e

2016-NXS5,

D,

FRN,

4.948%,

1/15/59

..................................

1,174,000

613,403

a

2016-C33,

D,

144A,

3.123%,

3/15/59

...................................

1,171,227

1,145,606

a,e

2015-C31,

E,

144A,

FRN,

4.672%,

11/15/48

..............................

1,550,000

984,064

e

WFRBS

Commercial

Mortgage

Trust

,

2014-C21,

B,

FRN,

4.213%,

8/15/47

...................................

1,544,467

1,523,466

2014-C23,

B,

FRN,

4.315%,

10/15/57

...................................

842,000

816,981

2013-C15,

C,

FRN,

4.152%,

8/15/46

...................................

985,000

905,831

2014-C21,

C,

FRN,

4.234%,

8/15/47

...................................

1,353,000

1,291,730

a

2013-C11,

D,

144A,

FRN,

4.296%,

3/15/45

...............................

1,284,115

1,162,087

a

2011-C4,

E,

144A,

FRN,

4.96%,

6/15/44

.................................

1,066,568

1,023,271

101,629,770

a

a

a

a

a

#### Total

#### Commercial

#### Mortgage-Backed

#### Securities

#### (Cost

#### $111,805,659)
...............

#### 101,629,770

#### Mortgage-Backed

#### Securities

#### 215.6%

#### Federal

#### National

#### Mortgage

#### Association
(FNMA)

#### Fixed

#### Rate

#### 171.3%
f

Uniform

Mortgage-Backed

Securities,

1.5%,

TBA,

4/25/41

.....................

11,000,000

9,891,993

f

Uniform

Mortgage-Backed

Securities,

2%,

TBA,

4/25/41

......................

18,000,000

16,562,366

f

Uniform

Mortgage-Backed

Securities,

2%,

TBA,

4/25/56

......................

75,000,000

60,427,734

f

Uniform

Mortgage-Backed

Securities,

2.5%,

TBA,

4/25/41

.....................

9,000,000

8,504,584

f

Uniform

Mortgage-Backed

Securities,

2.5%,

TBA,

4/25/56

.....................

48,000,000

40,395,078

f

Uniform

Mortgage-Backed

Securities,

3%,

TBA,

4/25/41

......................

4,000,000

3,820,803

f

Uniform

Mortgage-Backed

Securities,

3%,

TBA,

4/25/56

......................

26,000,000

22,840,791

f

Uniform

Mortgage-Backed

Securities,

3.5%,

TBA,

4/25/41

.....................

2,000,000

1,925,572

f

Uniform

Mortgage-Backed

Securities,

3.5%,

TBA,

4/25/56

.....................

24,000,000

22,005,082

f

Uniform

Mortgage-Backed

Securities,

4%,

TBA,

4/25/56

......................

8,000,000

7,550,064

f

Uniform

Mortgage-Backed

Securities,

4.5%,

TBA,

4/25/56

.....................

36,500,000

35,206,942

f

Uniform

Mortgage-Backed

Securities,

5%,

TBA,

4/25/56

......................

8,000,000

7,890,888

f

Uniform

Mortgage-Backed

Securities,

5.5%,

TBA,

4/25/56

.....................

168,000,000

168,913,525

f

Uniform

Mortgage-Backed

Securities,

6%,

TBA,

4/25/56

......................

180,000,000

183,848,239

f

Uniform

Mortgage-Backed

Securities,

6.5%,

TBA,

4/25/56

.....................

69,000,000

71,391,542

661,175,203

g

#### Government

#### National

#### Mortgage

#### Association
(GNMA)

#### Adjustable

#### Rate

#### 0.0%

#### †
GNMA

II,

5.375%,

(1-year

CMT

T-Note

+/-

MBS

Margin),

7/20/26

................

#### Government

#### National

#### Mortgage

#### Association
(GNMA)

#### Fixed

#### Rate

#### 44.3%
GNMA

I,

Single-family,

Year,

5.5%,

8/15/35

..............................

f

GNMA

II,

Single-family,

Year,

2%,

4/15/56

...............................

15,000,000

12,394,922

f

GNMA

II,

Single-family,

Year,

2.5%,

4/15/56

.............................

16,000,000

13,767,500

f

GNMA

II,

Single-family,

Year,

3%,

4/15/56

...............................

11,000,000

9,821,966

f

GNMA

II,

Single-family,

Year,

3.5%,

4/15/56

.............................

14,000,000

12,843,150

f

GNMA

II,

Single-family,

Year,

4%,

4/15/56

...............................

13,000,000

12,179,553

f

GNMA

II,

Single-family,

Year,

4.5%,

4/15/56

.............................

7,000,000

6,763,496

f

GNMA

II,

Single-family,

Year,

5%,

4/15/56

...............................

10,000,000

9,905,367

f

GNMA

II,

Single-family,

Year,

5.5%,

4/15/56

.............................

4,000,000

4,026,100

f

GNMA

II,

Single-family,

Year,

6%,

4/15/56

...............................

84,000,000

85,345,893

f

GNMA

II,

Single-family,

Year,

6.5%,

4/15/56

.............................

4,000,000

4,157,548

171,205,552

#### Total

#### Mortgage-Backed

#### Securities

#### (Cost

#### $835,750,734)

#### ...........................

#### 832,380,849
Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Residential

#### Mortgage-Backed

#### Securities

#### 16.8%

#### Financial

#### Services

#### 16.8%
a

A&D

Mortgage

Trust

,

2023-NQM2,

A1,

144A,

6.132%,

5/25/68

................................

$

957,737

$

956,210

2023-NQM4,

A1,

144A,

7.472%,

9/25/68

................................

1,076,117

1,085,582

2023-NQM5,

A1,

144A,

7.049%,

11/25/68

...............................

1,288,415

1,299,209

2024-NQM1,

A1,

144A,

6.195%,

2/25/69

................................

1,152,284

1,158,162

b

Alternative

Loan

Trust

,

2006-OA19

,

A1

,

FRN

,

3.97 %

,

(1-month

SOFR

+

0.294 %),

2/20/47

.........................................................

1,508,218

1,233,795

b

American

Home

Mortgage

Investment

Trust

,

2007-1

,

GA1C

,

FRN

,

3.983 %

,

(1-month

SOFR

+

0.304 %),

5/25/47

...........................................

4,682,429

2,842,643

a,e

Arroyo

Mortgage

Trust

,

2019-3

,

M1

,

144A,

FRN

,

4.204 %

,

10/25/48

..............

750,000

700,919

Bear

Stearns

ALT-A

Trust

,

b

2005-10,

11A1,

FRN,

4.293%,

(1-month

SOFR

+

0.614%),

1/25/36

.............

145,776

142,873

e

2005-8,

21A1,

FRN,

4.902%,

10/25/35

..................................

247,886

206,599

a

COLT

Mortgage

Loan

Trust

,

2023-3

,

A1

,

144A,

7.18 %

,

9/25/68

.................

1,602,067

1,612,501

a

Cross

Mortgage

Trust

,

2024-H1

,

A1

,

144A,

6.085 %

,

12/25/68

..................

1,226,110

1,232,109

Deutsche

Alt-B

Securities

Mortgage

Loan

Trust

,

2006-AB4

,

A4B

,

6.5 %

,

10/25/36

....

1,682,686

1,468,186

a,b

FHLMC

STACR

REMIC

Trust

,

2020-HQA2,

B2,

144A,

FRN,

11.376%,

(30-day

SOFR

Average

+

7.714%),

3/25/50

1,000,000

1,201,258

2020-HQA3,

B2,

144A,

FRN,

13.776%,

(30-day

SOFR

Average

+

10.114%),

7/25/50

916,000

1,205,573

2020-DNA4,

B2,

144A,

FRN,

13.776%,

(30-day

SOFR

Average

+

10.114%),

8/25/50

2,647,000

3,500,533

2021-DNA1,

B2,

144A,

FRN,

8.412%,

(30-day

SOFR

Average

+

4.75%),

1/25/51

..

1,330,000

1,487,968

a,b

FHLMC

STACR

Trust

,

2019-FTR3,

B2,

144A,

FRN,

8.576%,

(30-day

SOFR

Average

+

4.914%),

9/25/47

.

371,000

402,778

2019-FTR1,

B2,

144A,

FRN,

12.126%,

(30-day

SOFR

Average

+

8.464%),

1/25/48

2,681,000

3,167,400

2018-HQA2,

B2,

144A,

FRN,

14.776%,

(30-day

SOFR

Average

+

11.114%),

10/25/48

2,108,000

2,562,845

2019-DNA1,

B2,

144A,

FRN,

14.526%,

(30-day

SOFR

Average

+

10.864%),

1/25/49

4,520,000

5,545,094

2019-HQA2,

B2,

144A,

FRN,

15.026%,

(30-day

SOFR

Average

+

11.364%),

4/25/49

637,000

749,620

2019-DNA4,

B2,

144A,

FRN,

10.026%,

(30-day

SOFR

Average

+

6.364%),

10/25/49

1,070,000

1,183,275

e

FHLMC,

Structured

Pass-Through

Certificates

,

T-57,

2A1,

FRN,

4.891%,

7/25/43

......................................

8,253

8,069

T-59,

2A1,

FRN,

4.232%,

10/25/43

.....................................

4,192

3,585

FNMA

,

e

2003-W3,

1A4,

FRN,

4.87%,

8/25/42

...................................

10,615

10,347

e

2004-W2,

4A,

FRN,

5.03%,

2/25/44

....................................

1,852

1,827

d,e

2001-79,

BI,

IO,

FRN,

0.259%,

3/25/45

.................................

355,980

2,172

2003-34,

P1,

Strip,

4/25/43

...........................................

26,980

24,929

b

FNMA

Connecticut

Avenue

Securities

Trust

,

2016-C03,

1B,

FRN,

15.526%,

(30-day

SOFR

Average

+

11.864%),

10/25/28

.....

2,801,067

2,820,971

2016-C04,

1B,

FRN,

14.026%,

(30-day

SOFR

Average

+

10.364%),

1/25/29

......

775,511

795,982

2016-C06,

1B,

FRN,

13.026%,

(30-day

SOFR

Average

+

9.364%),

4/25/29

.......

501,224

520,378

a

2020-R01,

1B1,

144A,

FRN,

7.026%,

(30-day

SOFR

Average

+

3.364%),

1/25/40

..

347,000

351,855

a

2020-SBT1,

1B1,

144A,

FRN,

10.526%,

(30-day

SOFR

Average

+

6.864%),

2/25/40

3,455,000

3,603,329

a

2020-SBT1,

1M2,

144A,

FRN,

7.426%,

(30-day

SOFR

Average

+

3.764%),

2/25/40

1,887,000

1,930,283

2016-C03,

2B,

FRN,

16.526%,

(30-day

SOFR

Average

+

12.864%),

10/25/28

.....

465,059

468,828

a

2020-R02,

2B1,

144A,

FRN,

6.776%,

(30-day

SOFR

Average

+

3.114%),

1/25/40

..

311,000

315,056

a

2022-R02,

2M2,

144A,

FRN,

6.662%,

(30-day

SOFR

Average

+

3%),

1/25/42

.....

2,941,821

2,973,808

e

FNMA

REMIC

Trust

,

2003-W14,

2A,

FRN,

4.991%,

1/25/43

..................................

5,305

5,204

2003-W11,

A1,

FRN,

7.267%,

6/25/33

..................................

2004-W7,

A2,

FRN,

7.347%,

3/25/34

...................................

1,960

1,975

a

GS

Mortgage-Backed

Securities

Trust

,

2024-RPL4

,

A1

,

144A,

3.9 %

,

9/25/61

.......

542,879

530,559

b

HarborView

Mortgage

Loan

Trust

,

2005-2

,

1A

,

FRN

,

4.311 %

,

(1-month

SOFR

+

0.634 %),

5/19/35

..................................................

949,312

246,886

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Residential

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

a,b

Home

RE

Ltd.

,

2021-2

,

B1

,

144A,

FRN

,

7.812 %

,

(30-day

SOFR

Average

+

4.15 %),

1/25/34

.........................................................

$

1,000,000

$

1,008,824

a

HOMES

Trust

,

2024-NQM1

,

A1

,

144A,

5.915 %

,

7/25/69

......................

141,337

142,570

b

J.P.

Morgan

Alternative

Loan

Trust

,

2006-A6

,

1A1

,

FRN

,

4.113 %

,

(1-month

SOFR

+

0.434 %),

11/25/36

.................................................

839,284

736,956

a

J.P.

Morgan

Mortgage

Trust

,

2024-VIS2,

A1,

144A,

5.853%,

11/25/64

.................................

1,424,828

1,433,567

b

2024-9,

A11,

144A,

FRN,

5.012%,

(30-day

SOFR

Average

+

1.35%),

2/25/55

.....

1,490,329

1,494,110

MFA

Trust

,

2024-NPL1,

A1,

6.33%,

9/25/54

.......................................

532,288

533,343

a

2023-NQM3,

A1,

144A,

6.617%,

7/25/68

................................

294,967

295,782

a

2025-NQM3,

A1,

144A,

5.261%,

8/25/70

................................

933,126

932,797

a,b

Morgan

Stanley

Residential

Mortgage

Loan

Trust

,

2024-3,

AF,

144A,

FRN,

5.012%,

(30-day

SOFR

Average

+

1.35%),

7/25/54

......

834,546

836,101

2024-4,

AF,

144A,

FRN,

5.012%,

(30-day

SOFR

Average

+

1.35%),

9/25/54

......

757,003

758,246

a

PRET

LLC

,

2026-NPL1

,

A1

,

144A,

5.18 %

,

1/25/56

..........................

261,178

259,258

a

PRPM

LLC

,

2026-1

,

A1

,

144A,

5.185 %

,

2/25/31

............................

565,740

560,199

a

Saluda

Grade

Alternative

Mortgage

Trust

,

2024-RTL6

,

A1

,

144A,

7.439 %

,

7/25/30

...

509,000

512,748

a,b

Station

Place

Securitization

Trust

,

2025-1,

A,

144A,

FRN,

4.578%,

(1-month

SOFR

+

0.9%),

7/23/26

.............

1,458,000

1,469,891

2025-3,

A,

144A,

FRN,

4.578%,

(1-month

SOFR

+

0.9%),

9/23/26

.............

1,450,000

1,455,249

2025-7,

A,

144A,

FRN,

4.578%,

(1-month

SOFR

+

0.9%),

11/24/26

.............

1,448,000

1,451,330

b

Structured

Asset

Mortgage

Investments

II

Trust

,

2006-AR7

,

A1BG

,

FRN

,

3.913 %

,

(1-month

SOFR

+

0.234 %),

8/25/36

....................................

181,441

161,916

a,e

Towd

Point

Mortgage

Trust

,

2019-2

,

A2

,

144A,

FRN

,

3.75 %

,

12/25/58

............

862,000

781,257

b

WaMu

Mortgage

Pass-Through

Certificates

Trust

,

2005-AR8

,

2AC2

,

FRN

,

4.713 %

,

(1-month

SOFR

+

1.034 %),

7/25/45

....................................

418,331

403,087

64,788,601

a

a

a

a

a

#### Total

#### Residential

#### Mortgage-Backed

#### Securities

#### (Cost

#### $64,472,804)
.................

#### 64,788,601

#### Agency

#### Commercial

#### Mortgage-Backed

#### Securities

#### 32.5%

#### Financial

#### Services

#### 32.5%
FHLMC

,

3391,

Strip,

4/15/37

................................................

17,278

15,155

d

5457,

IO,

5%,

10/25/54

.............................................

3,666,208

737,945

e

3117,

AF,

FRN,

Zero

Cpn.,

2/15/36

.....................................

8,812

7,799

d

4953,

AI,

IO,

4%,

2/25/50

............................................

3,750,430

748,860

3369,

BO,

Strip,

9/15/37

.............................................

970

830

d

304,

C37,

IO,

3.5%,

12/15/27

.........................................

13,754

b

3065,

DC,

FRN,

8.5%,

(-3

x

30-day

SOFR

Average

+

19.517%),

3/15/35

........

626,514

647,461

d

4018,

DI,

IO,

4.5%,

7/15/41

..........................................

72,805

666

b,d

5003,

DS,

IO,

FRN,

2.324%,

(-1

x

30-day

SOFR

Average

+

5.986%),

8/25/50

.....

5,732,785

738,312

d

5529,

EI,

IO,

4.5%,

11/25/51

.........................................

3,245,974

713,769

b

3408,

EK,

FRN,

10.556%,

(-4

x

30-day

SOFR

Average

+

25.332%),

4/15/37

......

87,548

102,959

b

406,

F30,

FRN,

4.812%,

(30-day

SOFR

Average

+

1.15%),

10/25/53

...........

499,055

504,309

b

5391,

FC,

FRN,

4.762%,

(30-day

SOFR

Average

+

1.1%),

3/25/54

.............

407,010

410,236

b,d

4326,

GS,

IO,

FRN,

2.263%,

(-1

x

30-day

SOFR

Average

+

5.936%),

4/15/44

.....

6,629,260

655,479

d

5349,

IB,

IO,

4%,

12/15/46

...........................................

4,090,171

855,456

d

5050,

IM,

IO,

3.5%,

10/25/50

.........................................

8,186,325

1,605,976

d

4136,

IQ,

IO,

3.5%,

11/15/42

.........................................

2,398,137

236,636

d

5071,

IV,

IO,

3%,

12/25/50

...........................................

15,696,716

2,588,866

d

5459,

KI,

IO,

5%,

7/25/48

............................................

4,108,223

567,882

d

5121,

KI,

IO,

4%,

6/25/51

............................................

5,951,416

1,448,665

b,d

4915,

SD,

IO,

FRN,

2.274%,

(-1

x

30-day

SOFR

Average

+

5.936%),

9/25/49

.....

6,632,466

688,648

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Agency

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

FHLMC,

(continued)

b,d

5558,

SG,

IO,

FRN,

2.738%,

(-1

x

30-day

SOFR

Average

+

6.4%),

7/25/55

.......

$

18,743,516

$

1,768,991

d

5057,

TI,

IO,

3%,

11/25/50

...........................................

13,349,452

2,127,220

b,d

4839,

WS,

IO,

FRN,

2.313%,

(-1

x

30-day

SOFR

Average

+

5.986%),

8/15/56

....

6,186,204

839,721

a,b

FHLMC

Multi-family

Structured

Credit

Risk

Trust

,

2021-MN1,

M2,

144A,

FRN,

7.412%,

(30-day

SOFR

Average

+

3.75%),

1/25/51

...

1,051,000

1,092,312

2021-MN3,

M2,

144A,

FRN,

7.662%,

(30-day

SOFR

Average

+

4%),

11/25/51

....

2,289,000

2,373,066

FNMA

,

d

2020-31,

IO,

4.5%,

5/25/50

..........................................

7,895,926

1,411,465

d

2020-96,

IO,

3%,

1/25/51

............................................

6,667,495

1,151,666

d

2018-51,

BI,

IO,

5.5%,

7/25/38

........................................

1,260,920

55,794

d

2021-14,

CI,

IO,

4.5%,

11/25/49

.......................................

3,630,842

808,387

2008-53,

DO,

Strip,

7/25/38

..........................................

56,504

47,413

d

2012-104,

HI,

IO,

4%,

9/25/27

........................................

96,110

918

d

2023-49,

IA,

IO,

3%,

8/25/46

.........................................

6,806,997

865,476

b,d

2012-74,

IB,

IO,

FRN,

2.274%,

(-1

x

30-day

SOFR

Average

+

5.936%),

7/25/42

...

5,062,920

510,526

d

2023-49,

IB,

IO,

3.5%,

3/25/47

........................................

5,922,091

906,635

d

2021-3,

IB,

IO,

2.5%,

2/25/51

.........................................

5,382,269

901,758

d

2021-25,

IJ,

IO,

3.5%,

5/25/51

........................................

17,467,600

3,355,701

d

2020-20,

IK,

IO,

3.5%,

3/25/50

........................................

4,825,507

716,545

d

2015-58,

KI,

IO,

6%,

3/25/37

.........................................

2,820,435

442,929

2007-14,

KO,

Strip,

3/25/37

..........................................

1,601

1,367

b,d

2011-123,

KS,

IO,

FRN,

2.824%,

(-1

x

30-day

SOFR

Average

+

6.486%),

10/25/41

.

156,202

10,428

d

2020-62,

MI,

IO,

3.5%,

5/25/49

........................................

22,979,468

4,136,759

2006-84,

OT,

Strip,

9/25/36

..........................................

589

b,d

2022-51,

PS,

IO,

FRN,

2.288%,

(-1

x

30-day

SOFR

Average

+

5.95%),

8/25/52

...

9,102,931

855,226

b,d

2019-83,

QS,

IO,

FRN,

2.174%,

(-1

x

30-day

SOFR

Average

+

5.836%),

1/25/50

..

12,531,881

1,504,049

b,d

2019-51,

SA,

IO,

FRN,

2.274%,

(-1

x

30-day

SOFR

Average

+

5.936%),

9/25/49

..

5,387,840

682,628

b,d

2018-20,

SB,

IO,

FRN,

2.474%,

(-1

x

30-day

SOFR

Average

+

6.136%),

3/25/48

..

3,491,668

323,412

b,d

2023-57,

SC,

IO,

FRN,

2.224%,

(-1

x

30-day

SOFR

Average

+

5.886%),

10/25/49

.

4,899,526

478,696

a,b

FNMA

Multi-family

Connecticut

Avenue

Securities

Trust

,

2019-01

,

M10

,

144A,

FRN

,

7.026 %

,

(30-day

SOFR

Average

+

3.364 %),

10/25/49

......................

2,467,410

2,507,571

GNMA

,

d

2012-136,

IO,

3.5%,

11/20/42

.........................................

4,102,564

516,509

d

2014-76,

IO,

5%,

5/20/44

............................................

1,558,342

316,469

1.6%,

2/20/49

....................................................

7,829,467

514,624

d,e

2024-32,

IO,

FRN,

0.7%,

6/16/63

......................................

16,551,479

847,932

d,e

2016-H24,

IO,

FRN,

2.046%,

9/20/66

...................................

5,283,916

319,175

d,e

2017-H09,

IO,

FRN,

1.86%,

4/20/67

....................................

3,925,019

114,371

d

2014-174,

AI,

IO,

3%,

11/16/29

........................................

450,103

9,342

d,e

2014-H21,

AI,

IO,

FRN,

2.113%,

10/20/64

...............................

3,546,195

172,732

d,e

2015-H04,

AI,

IO,

FRN,

1.921%,

12/20/64

...............................

4,197,755

131,164

d,e

2015-H13,

AI,

IO,

FRN,

2.365%,

6/20/65

................................

3,548,332

189,606

d,e

2015-H14,

AI,

IO,

FRN,

2.67%,

6/20/65

.................................

7,492,963

410,375

d,e

2015-H22,

AI,

IO,

FRN,

2.432%,

9/20/65

................................

5,276,092

290,755

d,e

2016-H03,

AI,

IO,

FRN,

1.957%,

1/20/66

................................

3,034,937

127,592

d,e

2016-H10,

AI,

IO,

FRN,

1.762%,

4/20/66

................................

5,660,122

162,310

d,e

2016-H19,

AI,

IO,

FRN,

2.593%,

9/20/66

................................

3,953,908

169,520

d,e

2020-H18,

AI,

IO,

FRN,

2.275%,

9/20/70

................................

14,091,811

900,968

b,d

2023-7,

AS,

IO,

FRN,

3.227%,

(-1

x

30-day

SOFR

Average

+

6.9%),

1/20/53

.....

20,898,221

1,497,815

b,d

2023-56,

AS,

IO,

FRN,

2.487%,

(-1

x

30-day

SOFR

Average

+

6.16%),

4/20/53

...

21,493,182

1,359,300

d

2014-182,

BI,

IO,

4%,

1/20/39

........................................

2,615,813

136,771

d,e

2017-H04,

BI,

IO,

FRN,

2.427%,

2/20/67

................................

3,714,528

160,727

d,e

2017-H23,

BI,

IO,

FRN,

1.942%,

11/20/67

...............................

3,336,968

121,996

d,e

2020-H05,

BI,

IO,

FRN,

2.696%,

3/20/70

................................

1,799,030

82,421

d

2009-121,

CI,

IO,

4.5%,

12/16/39

......................................

2,448,861

382,934

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Agency

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

GNMA,

(continued)

d

2022-125,

CI,

IO,

5%,

6/20/52

........................................

$

7,677,817

$

1,462,626

d,e

2015-H20,

CI,

IO,

FRN,

2.53%,

8/20/65

.................................

4,705,069

247,124

d,e

2016-H06,

DI,

IO,

FRN,

2.222%,

7/20/65

................................

2,676,217

98,616

d,e

2020-H18,

DI,

IO,

FRN,

2.684%,

11/20/70

...............................

1,431,964

69,462

b,d

2023-181,

DS,

IO,

FRN,

2.327%,

(-1

x

30-day

SOFR

Average

+

6%),

11/20/53

....

20,144,208

1,092,962

b,d

2021-117,

ES,

IO,

FRN,

2.51%,

(-1

x

1-month

SOFR

+

6.186%),

7/20/51

........

5,397,760

776,895

b,d

2023-173,

ES,

IO,

FRN,

3.277%,

(-1

x

30-day

SOFR

Average

+

6.95%),

11/20/53

..

6,301,010

475,667

b,d

2024-4,

ES,

IO,

FRN,

3.277%,

(-1

x

30-day

SOFR

Average

+

6.95%),

1/20/54

....

9,185,683

644,450

b

2023-152,

FB,

FRN,

4.823%,

(30-day

SOFR

Average

+

1.15%),

4/20/51

.........

865,588

883,458

d

2021-176,

GI,

IO,

3%,

10/20/51

.......................................

6,195,733

931,846

d

2024-4,

GI,

IO,

5%,

2/20/53

..........................................

3,166,098

780,271

d,e

2016-H27,

GI,

IO,

FRN,

2.222%,

12/20/66

...............................

6,668,491

424,743

d,e

2017-H08,

GI,

IO,

FRN,

1.771%,

2/20/67

................................

4,840,038

432,612

d,e

2015-H10,

HI,

IO,

FRN,

2.299%,

4/20/65

................................

3,309,140

194,164

b,d

2025-62,

HS,

IO,

FRN,

2.41%,

(-1

x

1-month

SOFR

+

6.086%),

11/20/47

........

6,455,072

766,546

b,d

2024-51,

HS,

IO,

FRN,

2.327%,

(-1

x

30-day

SOFR

Average

+

6%),

3/20/54

......

11,367,315

643,058

b,d

2024-110,

HS,

IO,

FRN,

2.977%,

(-1

x

30-day

SOFR

Average

+

6.65%),

7/20/54

..

11,887,773

908,473

d,e

2025-H14,

IA,

IO,

FRN,

1.771%,

5/20/75

................................

22,858,984

683,081

d

2020-138,

IB,

IO,

2.5%

,

9/20/50

.......................................

20,203,406

2,889,950

d,e

2023-H16,

ID,

IO,

FRN,

0.344%,

4/20/72

................................

8,730,875

285,756

d

2014-102,

IG,

IO,

3.5%,

3/16/41

.......................................

106,802

1,217

d

2022-30,

IG,

IO,

3%,

2/20/52

.........................................

6,861,828

1,034,605

d

2024-4,

IG,

IO,

5%,

12/20/52

.........................................

4,743,643

888,894

d

2013-39,

IJ,

IO,

4.5%,

3/20/43

........................................

3,473,491

517,043

d,e

2016-H13,

IK,

IO,

FRN,

2.634%,

6/20/66

................................

2,292,519

210,492

d

2021-89,

IL,

IO,

4.5%,

5/20/51

........................................

6,069,235

1,415,408

d

2021-8,

IP,

IO,

2.5%,

1/20/51

.........................................

22,723,815

3,293,715

d

2021-188,

IW,

IO,

3%,

10/20/51

.......................................

6,814,347

1,152,723

d,e

2021-H12,

IY,

IO,

FRN,

0.058%,

8/20/71

................................

37,376,413

801,676

d

2020-175,

JI,

IO,

3.5%,

11/20/50

......................................

8,727,280

1,653,767

d,e

2016-H24,

JI,

IO,

FRN,

2.701%,

11/20/66

................................

1,793,114

114,940

d,e

2018-H19,

JI,

IO,

FRN,

2.304%,

10/20/68

................................

5,525,767

190,506

d,e

2022-H04,

JI,

IO,

FRN,

0.759%,

2/20/72

.................................

17,888,812

871,035

b

2023-140,

JS,

FRN,

6.91%,

(-2

x

30-day

SOFR

Average

+

16.05%),

9/20/53

.....

701,638

711,680

d

2015-52,

KI,

IO,

3.5%,

11/20/40

.......................................

616,943

18,376

d

2025-214,

KI,

IO,

5.5%,

12/20/55

......................................

4,793,095

1,009,673

d,e

2017-H03,

KI,

IO,

FRN,

2.495%,

1/20/67

................................

5,042,495

435,450

b,d

2020-96,

KS,

IO,

FRN,

2.36%,

(-1

x

1-month

SOFR

+

6.036%),

7/20/50

.........

11,334,886

1,440,590

d

2016-75,

LI,

IO,

6%,

1/20/40

.........................................

1,674,263

230,396

d

2015-89,

LI,

IO,

5%,

12/20/44

.........................................

2,757,137

481,200

b,d

2024-126,

LS,

IO,

FRN,

2.977%,

(-1

x

30-day

SOFR

Average

+

6.65%),

8/20/54

...

22,568,279

1,752,316

d

2012-38,

MI,

IO,

4%,

3/20/42

.........................................

4,246,315

724,961

d

2015-53,

MI,

IO,

4%,

4/16/45

.........................................

2,417,198

472,518

d

2021-7,

MI,

IO,

2.5%,

1/20/51

.........................................

10,187,729

1,501,113

d,e

2017-H06,

MI,

IO,

FRN,

2.232%,

2/20/67

................................

5,325,640

208,920

d,e

2017-H10,

MI,

IO,

FRN,

1.785%,

4/20/67

................................

4,073,348

111,743

b,d

2020-112,

MS,

IO,

FRN,

2.51%,

(-1

x

1-month

SOFR

+

6.186%),

8/20/50

........

4,091,341

548,761

d

2021-97,

NI,

IO,

2.5%,

8/20/49

........................................

7,802,874

893,194

d

2020-123,

NI,

IO,

2.5%,

8/20/50

.......................................

12,783,827

1,925,515

d

2021-76,

NI,

IO,

3%,

8/20/50

.........................................

8,864,213

1,499,079

d,e

2016-H23,

NI,

IO,

FRN,

2.729%,

10/20/66

...............................

5,748,512

283,315

d,e

2017-H08,

NI,

IO,

FRN,

1.92%,

3/20/67

.................................

3,193,946

116,032

b,d

2024-4,

NS,

IO,

FRN,

2.077%,

(-1

x

30-day

SOFR

Average

+

5.75%),

1/20/54

....

12,667,690

814,970

d

2013-6,

OI,

IO,

5%,

1/20/43

..........................................

4,451,156

876,115

d,e

2016-H07,

PI,

IO,

FRN,

2.204%,

3/20/66

................................

3,713,780

251,690

b

2023-66,

PS,

FRN,

6.193%,

(-3

x

30-day

SOFR

Average

+

15.375%),

5/20/53

....

2,273,651

2,218,419

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

a

a

#### Principal

#### Amount
a

#### Value
a

a

#### a
a

#### Agency

#### Commercial

#### Mortgage-Backed

#### Securities
(continued)

#### Financial

#### Services
(continued)

GNMA,

(continued)

d

2013-51,

QI,

IO,

5%,

2/20/43

.........................................

$

1,550,825

$

156,797

d,e

2016-H18,

QI,

IO,

FRN,

2.814%,

6/20/66

................................

3,328,375

195,702

b,d

2024-64,

QS,

IO,

FRN,

2.327%,

(-1

x

30-day

SOFR

Average

+

6%),

4/20/54

......

31,492,694

2,193,258

b,d

2023-19,

S,

IO,

FRN,

2.26%,

(-1

x

1-month

SOFR

+

5.936%),

11/20/49

.........

20,653,340

2,295,825

b,d

2022-153,

S,

IO,

FRN,

2.377%,

(-1

x

30-day

SOFR

Average

+

6.05%),

5/20/50

....

8,817,934

860,832

b,d

2024-11,

S,

IO,

FRN,

2.727%,

(-1

x

30-day

SOFR

Average

+

6.4%),

1/20/54

......

6,933,491

441,811

b,d

2013-87,

SA,

IO,

FRN,

2.41%,

(-1

x

1-month

SOFR

+

6.086%),

6/20/43

.........

5,134,480

563,562

b,d

2020-47,

SA,

IO,

FRN,

2.21%,

(-1

x

1-month

SOFR

+

5.886%),

5/20/44

.........

8,188,183

841,012

b,d

2014-119,

SA,

IO,

FRN,

1.81%,

(-1

x

1-month

SOFR

+

5.486%),

8/20/44

........

2,332,798

216,585

b,d

2024-7,

SA,

IO,

FRN,

2.727%,

(-1

x

30-day

SOFR

Average

+

6.4%),

1/20/54

.....

7,022,289

448,917

b,d

2010-20,

SC,

IO,

FRN,

2.36%,

(-1

x

1-month

SOFR

+

6.036%),

2/20/40

.........

326,404

32,906

b,d

2024-96,

SC,

IO,

FRN,

2.977%,

(-1

x

30-day

SOFR

Average

+

6.65%),

6/20/54

...

17,304,885

1,416,455

b,d

2016-80,

SD,

IO,

FRN,

2.31%,

(-1

x

1-month

SOFR

+

5.986%),

6/20/46

.........

5,117,666

622,810

b,d

2025-120,

SD,

IO,

FRN,

2.21%,

(-1

x

1-month

SOFR

+

5.886%),

10/20/49

.......

15,439,300

1,690,055

b,d

2019-121,

SD,

IO,

FRN,

2.21%,

(-1

x

1-month

SOFR

+

5.886%),

10/20/49

.......

6,517,203

763,116

b,d

2019-125,

SG,

IO,

FRN,

2.26%,

(-1

x

1-month

SOFR

+

5.936%),

10/20/49

.......

6,719,469

759,419

b,d

2022-209,

SG,

IO,

FRN,

1.927%,

(-1

x

30-day

SOFR

Average

+

5.6%),

12/20/52

..

26,918,467

1,655,176

b,d

2022-120,

SH,

IO,

FRN,

2.377%,

(-1

x

30-day

SOFR

Average

+

6.05%),

7/20/52

..

13,573,489

1,153,760

b,d

2023-66,

SH,

IO,

FRN,

2.477%,

(-1

x

30-day

SOFR

Average

+

6.15%),

5/20/53

...

12,125,085

868,006

b,d

2011-156,

SK,

IO,

FRN,

2.81%,

(-1

x

1-month

SOFR

+

6.486%),

4/20/38

........

4,385,402

466,311

b,d

2021-98,

SK,

IO,

FRN,

2.51%,

(-1

x

1-month

SOFR

+

6.186%),

6/20/51

.........

7,395,910

989,490

b,d

2023-103,

SK,

IO,

FRN,

2.327%,

(-1

x

30-day

SOFR

Average

+

6%),

7/20/53

.....

11,588,874

718,848

b,d

2023-13,

SL,

IO,

FRN,

2.577%,

(-1

x

30-day

SOFR

Average

+

6.25%),

1/20/53

....

16,156,164

1,105,358

b,d

2021-59,

SM,

IO,

FRN,

2.51%,

(-1

x

1-month

SOFR

+

6.186%),

4/20/51

.........

3,413,435

437,907

b,d

2021-77,

SM,

IO,

FRN,

2.51%,

(-1

x

1-month

SOFR

+

6.186%),

5/20/51

.........

10,599,926

1,413,555

b,d

2013-182,

SP,

IO,

FRN,

2.91%,

(-1

x

1-month

SOFR

+

6.586%),

12/20/43

.......

2,091,696

280,720

b,d

2023-20,

SP,

IO,

FRN,

3.327%,

(-1

x

30-day

SOFR

Average

+

7%),

2/20/53

......

9,367,110

705,970

b,d

2019-110,

SQ,

IO,

FRN,

2.26%,

(-1

x

1-month

SOFR

+

5.936%),

9/20/49

........

4,562,367

503,475

b,d

2023-24,

SQ,

IO,

FRN,

2.577%,

(-1

x

30-day

SOFR

Average

+

6.25%),

2/20/53

...

5,346,976

368,892

b,d

2024-30,

SU,

IO,

FRN,

2.177%,

(-1

x

30-day

SOFR

Average

+

5.85%),

2/20/54

...

17,435,505

1,095,496

d

2021-182,

TI,

IO,

3.5%,

10/20/51

......................................

3,838,783

711,875

d,e

2015-H23,

TI,

IO,

FRN,

1.967%,

9/20/65

................................

2,796,282

114,919

d

2020-162,

UI,

IO,

2.5%,

10/20/50

......................................

6,795,960

982,093

b,d

2024-30,

WS,

IO,

FRN,

2.127%,

(-1

x

30-day

SOFR

Average

+

5.8%),

2/20/54

....

13,842,542

752,389

d,e

2015-H16,

XI,

IO,

FRN,

2.647%,

7/20/65

................................

1,738,827

105,542

125,381,316

a

a

a

a

a

#### Total

#### Agency

#### Commercial

#### Mortgage-Backed

#### Securities

#### (Cost

#### $123,040,948)

#### ........

#### 125,381,316

#### Total

#### Long

#### Term

#### Investments

#### (Cost

#### $1,153,403,999)

#### .............................

#### 1,142,683,683

#### a
a

a

a

#### Short

#### Term

#### Investments

#### 16.6%

#### Shares
a

#### Management

#### Investment

#### Companies

#### 13.8%
h,i

Putnam

Short

Term

Investment

Fund,

Class

P,

3.821%

.......................

53,474,576

53,474,576

#### Total

#### Management

#### Investment

#### Companies

#### (Cost

#### $53,474,576)
....................

#### 53,474,576

#### Principal

#### Amount

#### U.S.

#### Government

#### and

#### Agency

#### Securities

#### 2.8%
j,k

U.S.

Treasury

Bills

,

3.47%,

4/23/26

...................................................

2,200,000

2,195,127

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

#### Short

#### Term

#### Investments
(continued)

a

a

#### Principal

#### Amount
a

#### Value

#### U.S.

#### Government

#### and

#### Agency

#### Securities
(continued)

j,k

U.S.

Treasury

Bills,

(continued)

3.58%,

7/16/26

...................................................

$

8,500,000

$

8,410,440

10,605,567

#### Total

#### U.S.

#### Government

#### and

#### Agency

#### Securities

#### (Cost

#### $10,606,198)

#### .................

#### 10,605,567

#### Total

#### Short

#### Term

#### Investments

#### (Cost

#### $64,080,774)

#### ................................

#### 64,080,143

#### a

#### Total

#### Investments

#### (Cost

#### $1,217,484,773)

#### 312.6%

#### ................................

#### $1,206,763,826

#### TBA

#### Sale

#### Commitments

#### (64.8)%

#### ...............................................

#### (250,048,811)

#### Other

#### Assets,

#### less

#### Liabilities

#### (147.8)%

#### .........................................

#### (570,614,099)

#### Net

#### Assets

#### 100.0%

#### ...........................................................

#### $386,100,916
a

a

#### a
a

#### TBA

#### Sale

#### Commitments

#### (64.8)%

#### Mortgage-Backed

#### Securities

#### (64.8)%

#### Federal

#### National

#### Mortgage

#### Association
(FNMA)

#### Fixed

#### Rate

#### (45.8)%
l

Uniform

Mortgage-Backed

Securities

,

2.5%,

TBA,

4/25/56

..................................................

(5,000,000)

(4,234,766)

4.5%,

TBA,

4/25/56

..................................................

(4,000,000)

(3,836,641)

5.5%,

TBA,

4/25/56

..................................................

(58,000,000)

(58,389,687)

6%,

TBA,

4/25/56

...................................................

(108,000,000)

(110,445,373)

(176,906,467)

#### Government

#### National

#### Mortgage

#### Association
(GNMA)

#### Fixed

#### Rate

#### (19.0)%
l

GNMA

II,

Single-family,

Year,

6%,

4/15/56

...............................

(72,000,000)

(73,142,344)

#### Total

#### TBA

#### Sale

#### Commitments

#### (Cost

#### $(250,130,742))

#### .............................

#### $(250,048,811)
†

Rounds

to

less

than

0.1%

of

net

assets.

a

Security

was

purchased

pursuant

to

Rule

144A

or

Regulation

S

under

the

Securities

Act

of

1933. 144A

securities

may

be

sold

in

transactions

exempt

from

registration

only

to

qualified

institutional

buyers

or

in

a

public

offering

registered

under

the

Securities

Act

of

1933. Regulation

S

securities

cannot

be

sold

in

the

United

States

without

either

an

effective

registration

statement

filed

pursuant

to

the

Securities

Act

of

1933,

or

pursuant

to

an

exemption

from

registration.

At

March

31,

2026,

the

aggregate

value

of

these

securities

was

$125,430,001,

representing

32.5%

of

net

assets.

b

The

coupon

rate

shown

represents

the

rate

inclusive

of

any

caps

or

floors,

if

applicable,

in

effect

at

period

end.

c

Defaulted

security

or

security

for

which

income

has

been

deemed

uncollectible.

See

Note

.

d

Investment

in

an

interest-only

security

entitles

holders

to

receive

only

the

interest

payment

on

the

underlying

instruments.

The

principal

amount

shown

is

the

notional

amount

of

the

underlying

instruments.

e

Adjustable

rate

security

with

an

interest

rate

that

is

not

based

on

a

published

reference

index

and

spread.

The

rate

is

based

on

the

structure

of

the

agreement

and

current

market

conditions.

The

coupon

rate

shown

represents

the

rate

at

period

end.

f

Security

purchased

on

a

to-be-announced

(TBA)

basis.

See

Note

(d).

g

Adjustable

Rate

Mortgage-Backed

Security

(ARM);

the

rate

shown

is

the

effective

rate

at

period

end.

ARM

rates

are

not

based

on

a

published

reference

rate

and

spread;

they

are

based

on

the

weighted

average

rates

of

the

underlying

mortgage

loans,

less

the

applicable

servicing

and

guarantee

fees

(MBS

margin).

h

See

Note

(g)

regarding

investments

in

affiliated

management

investment

companies.

i

The

rate

shown

is

the

annualized

seven-day

effective

yield

at

period

end.

j

The

rate

shown

represents

the

yield

at

period

end.

k

A

portion

or

all

of

the

security

has

been

segregated

as

collateral

for

certain

derivative

contracts

and

TBA

securities.

At

March

31,

2026,

the

aggregate

value

of

these

securities

pledged

amounted

to

$7,876,656,

representing

2.0%

of

net

assets.

l

Security

sold

on

a

to-be-announced

(TBA)

basis

resulting

in

a

short

position.

As

such,

the

Fund

is

not

subject

to

fees

and

expenses

associated

with

short

sale

transactions.

See

Note

(d).

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

At

March

31,

2026,

the

Fund

had

the

following futures

contracts

outstanding.

See

Note

(e).

At

March

31,

2026,

the

Fund

had

the

following forward

premium

swap

options contracts

outstanding.

See

Note

(e).

#### Futures

#### Contracts

#### Description

#### Type

#### Number

#### of

#### Contracts

#### Notional

#### Amount

#### \*

#### Expiration

#### Date

#### Value/

#### Unrealized

#### Appreciation
(Depreciation)

#### Interest

#### rate

#### contracts
U.S.

Treasury

Year

Notes

.....................

Short

$

36,302,930

6/30/26

$

264,986

Total

Futures

Contracts

......................................................................

$264,986

\*

As

of

period

end.

#### Forward

#### Premium

#### Swap

#### Option

#### Contracts

#### Fixed

#### right

#### or

#### obligation

#### to

#### receive

#### or

#### (pay)/

#### Floating

#### rate

#### index/Maturity

#### date

#### Counter

#### par

#### t

#### y

#### Expiration

#### date/strike

#### Notional/

#### Contract

#### amount

#### \*

#### Premium

#### receivable/
(payable)

#### Unrealized

#### appreciation/
(depreciation)

#### a
3.55%/1-day

SOFR/May-28/(Written)

BOFA

5/20/26

/

3.55%

213,943,700

$

(1,904,099)

$

1,296,681

(3.56%)/1-day

SOFR/May-28/(Purchased)

BOFA

5/20/26

/

3.56%

213,943,700

353,007

475,049

(4.225%)/1-day

SOFR/Nov-36/(Purchased)

BOFA

11/23/26

/

4.225%

26,602,700

1,362,058

(989,490)

3.725%/1-day

SOFR/Nov-36/(Purchased)

BOFA

11/23/26

/

3.725%

26,602,700

1,300,872

(858,161)

(3.428%)/1-day

SOFR/Aug-37/(Purchased)

BOFA

8/13/27

/

3.428%

23,866,000

1,373,488

61,249

3.428%/1-day

SOFR/Aug-37/(Purchased)

BOFA

8/13/27

/

3.428%

23,866,000

1,373,488

(971,131)

3.61%/1-day

SOFR/Oct-34/(Purchased)

BOFA

10/09/29

/

3.61%

17,140,800

672,777

(266,858)

(3.61%)/1-day

SOFR/Oct-34/(Purchased)

BOFA

10/09/29

/

3.61%

17,140,800

672,777

(15,240)

4.2%/1-day

SOFR/Aug-60/(Purchased)

BOFA

8/26/30

/

4.2%

2,728,900

340,294

(39,426)

(4.2%)/1-day

SOFR/Aug-60/(Purchased)

BOFA

8/26/30

/

4.2%

2,728,900

340,294

(31,425)

(4.608%)/1-day

SOFR/May-56/(Purchased)

CITI

5/26/26

/

4.608%

2,873,200

104,297

(96,685)

3.965%/1-day

SOFR/Mar-38/(Purchased)

DBAB

3/06/28

/

3.965%

11,892,700

648,152

(209,982)

(3.965%)/1-day

SOFR/Mar-38/(Purchased)

DBAB

3/06/28

/

3.965%

11,892,700

648,152

(142,395)

4.33%/1-day

SOFR/May-52/(Purchased)

DBAB

5/19/32

/

4.33%

3,640,400

455,960

(84,469)

(4.33%)/1-day

SOFR/May-52/(Purchased)

DBAB

5/19/32

/

4.33%

3,640,400

455,960

(52,240)

2.35%/1-day

SOFR/Mar-59/(Purchased)

GSCO

3/12/29

/

2.35%

13,681,500

797,632

(602,552)

(4.01%)/1-day

SOFR/Mar-52/(Purchased)

MCM

3/29/32

/

4.01%

2,467,800

295,889

14,593

4.01%/1-day

SOFR/Mar-52/(Purchased)

MCM

3/29/32

/

4.01%

2,467,800

295,889

(90,244)

(4.825%)/1-day

SOFR/May-57/(Purchased)

NATW

4/30/27

/

4.825%

12,604,500

456,283

(205,733)

#### Unrealized

#### appreciation

#### 1,847,572

#### Unrealized
(depreciation)

#### (4,656,031)

#### Total

#### $(2,808,459)
\*

In

U.S.

dollars

unless

otherwise

indicated.

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

At

March

31,

2026,

the

Fund

had

the

following credit

default

swap

contracts outstanding.

See

Note

1(e).

#### Credit

#### Default

#### Swap

#### Contracts

#### Description

#### Periodic

#### Payment

#### Rate

#### Received
(Paid)

#### Payment

#### Frequency

#### Counter-

#### party

#### Maturity

#### Date

#### Notional

#### Amount

#### a

#### Value

#### Upfront

#### Payments
(Receipts)

#### Unrealized

#### Appreciation
(Depreciation)

#### Rating

#### b

#### OTC

#### Swap

#### Contracts

#### to

#### Buy

#### Protection

#### c

#### Traded

#### Index
CMBX.NA.BB.10

(5.00)%

Monthly

CITI

11/17/59

711,000

$

391,768

$

286,537

$

105,231

CMBX.NA.BB.10

(5.00)%

Monthly

MLCO

11/17/59

31,000

17,081

1,764

15,317

CMBX.NA.BB.13

(5.00)%

Monthly

GSCO

12/16/72

3,448,000

1,355,639

1,281,422

74,217

CMBX.NA.BB.6

.

(5.00)%

Monthly

GSCO

5/11/63

501,000

60,834

22,574

38,260

CMBX.NA.BB.6

.

(5.00)%

Monthly

JPHQ

5/11/63

216,000

26,228

111,197

(84,969)

CMBX.NA.BB.8

.

(5.00)%

Monthly

CITI

10/17/57

65,000

25,918

28,145

(2,227)

CMBX.NA.BB.8

.

(5.00)%

Monthly

GSCO

10/17/57

130,000

51,835

53,080

(1,245)

CMBX.NA.BB.8

.

(5.00)%

Monthly

MSCO

10/17/57

2,165,000

863,255

950,911

(87,656)

CMBX.

NA.BBB-.10

..

(3.00)%

Monthly

CITI

11/17/59

2,354,000

643,843

707,526

(63,683)

CMBX.

NA.BBB-.10

..

(3.00)%

Monthly

MSCO

11/17/59

1,792,000

490,131

579,466

(89,335)

CMBX.

NA.BBB-.11

..

(3.00)%

Monthly

GSCO

11/18/54

3,086,000

376,492

385,335

(8,843)

CMBX.

NA.BBB-.12

..

(3.00)%

Monthly

CITI

8/17/61

4,531,000

883,168

1,285,860

(402,692)

CMBX.

NA.BBB-.12

..

(3.00)%

Monthly

GSCO

8/17/61

1,017,000

198,231

184,586

13,645

CMBX.

NA.BBB-.13

..

(3.00)%

Monthly

GSCO

12/16/72

2,034,000

423,156

426,461

(3,305)

CMBX.

NA.BBB-.13

..

(3.00)%

Monthly

JPHQ

12/16/72

1,242,000

258,388

240,586

17,802

CMBX.NA.BBB-.8

(3.00)%

Monthly

CITI

10/17/57

784,000

141,097

151,449

(10,352)

CMBX.NA.BBB-.8

(3.00)%

Monthly

MSCO

10/17/57

1,274,000

229,284

262,257

(32,973)

CMBX.NA.BBB-.9

(3.00)%

Monthly

MSCO

9/17/58

1,017,000

240,464

182,679

57,785

#### Contracts

#### to

#### Sell

#### Protection

#### c,d

#### Traded

#### Index
CMBX.NA.A.13

.

2.00%

Monthly

MLCO

12/16/72

2,026,000

(130,655)

(266,877)

136,222

Investment

Grade

CMBX.NA.BB.10

5.00%

Monthly

JPHQ

11/17/59

360,000

(198,364)

(28,886)

(169,478)

Non-

Investment

Grade

CMBX.NA.BB.13

5.00%

Monthly

CITI

12/16/72

2,413,000

(948,711)

(1,031,696)

82,985

Non-

Investment

Grade

CMBX.NA.BB.6

.

5.00%

Monthly

CITI

5/11/63

1,462,000

(177,524)

(254,204)

76,680

Non-

Investment

Grade

CMBX.NA.BB.6

.

5.00%

Monthly

GSCO

5/11/63

31,000

(3,765)

(5,382)

1,617

Non-

Investment

Grade

CMBX.NA.BB.6

.

5.00%

Monthly

MLCO

5/11/63

1,670,000

(202,779)

(186,736)

(16,043)

Non-

Investment

Grade

CMBX.

NA.BBB-.16

..

3.00%

Monthly

CITI

4/17/65

140,000

(25,655)

(31,824)

6,169

Investment

Grade

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

At

March

31,

2026,

the

Fund

had

the

following

interest

rate

swap

contracts

outstanding.

See

Note

(e).

#### Credit

#### Default

#### Swap

#### Contracts
(continued)

#### Description

#### Periodic

#### Payment

#### Rate

#### Received
(Paid)

#### Payment

#### Frequency

#### Counter-

#### party

#### Maturity

#### Date

#### Notional

#### Amount

#### a

#### Value

#### Upfront

#### Payments
(Receipts)

#### Unrealized

#### Appreciation
(Depreciation)

#### Rating

#### b

#### OTC

#### Swap

#### Contracts
(continued)

#### to

#### Sell

#### Protection

#### c,d
(continued)

#### Traded

#### Index
(continued)

CMBX.

NA.BBB-.16

..

3.00%

Monthly

GSCO

4/17/65

141,000

$

(25,838)

$

(28,955)

$

3,117

Investment

Grade

CMBX.

NA.BBB-.16

..

3.00%

Monthly

MSCO

4/17/65

69,000

(12,645)

(15,685)

3,040

Investment

Grade

Total

Credit

Default

Swap

Contracts

........................................

$4,950,876

$5,291,590

$(340,714)

a

In

U.S.

dollars

unless

otherwise

indicated.

For

contracts

to

sell

protection,

the

notional

amount

is

equal

to

the

maximum

potential

amount

of

the

future

payments

and

no

recourse

provisions

have

been

entered

into

in

association

with

the

contracts.

b

Based

on

Standard

and

Poor's

(S&P)

Rating

for

single

name

swaps

and

internal

ratings

for

index

swaps.

Internal

ratings

based

on

mapping

into

equivalent

ratings

from

external

vendors.

c

Performance

triggers

for

settlement

of

contract

include

default,

bankruptcy

or

restructuring

for

single

name

swaps,

and

failure

to

pay

or

bankruptcy

of

the

underlying

securities

for

traded

index

swaps.

d

The

fund

enters

contracts

to

sell

protection

to

create

a

long

credit

position.

#### Interest

#### Rate

#### Swap

#### Contracts

#### Description

#### Payment

#### Frequency

#### Maturity

#### Date

#### Notional

#### Amount

#### \*

#### Value

#### Upfront

#### Payments
(Receipts)

#### Unrealized

#### Appreciation
(Depreciation)

aa

#### aa

#### Centrally

#### Cleared

#### Swap

#### Contracts
Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

3.3%

.....

Annual

3/18/28

858,772,000

$

5,676,708

$

(735,794)

$

6,412,502

Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

3.5%

.....

Annual

6/17/28

50,426,000

111,711

160,276

(48,565)

Receive

Fixed

3.45%

..

Annual

Pay

Floating

1-day

SOFR

............

Annual

3/18/31

503,957,000

(4,072,138)

155,552

(4,227,690)

Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

3.55%

....

Annual

6/17/31

20,162,000

76,234

120,086

(43,852)

Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

3.75%

....

Annual

3/18/36

298,370,000

2,916,377

1,081,364

1,835,013

Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

3.8%

.....

Annual

6/17/36

6,234,000

39,408

39,408

—

Receive

Fixed

4.1%

...

Annual

Pay

Floating

1-day

SOFR

............

Annual

3/18/56

17,710,000

(103,482)

18,142

(121,624)

Putnam

Mortgage

Securities

Fund

Schedule

of

Investments

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

#### Interest

#### Rate

#### Swap

#### Contracts
(continued)

#### Description

#### Payment

#### Frequency

#### Maturity

#### Date

#### Notional

#### Amount\*

#### Value

#### Upfront

#### Payments
(Receipts)

#### Unrealized

#### Appreciation
(Depreciation)

aa

#### aa

#### Centrally

#### Cleared

#### Swap

#### Contracts
(continued)

Receive

Floating

1-day

SOFR

..............

Annual

Pay

Fixed

4.05%

....

Annual

6/17/56

5,829,000

$

87,112

$

104,114

$

(17,002)

Total

Interest

Rate

Swap

Contracts

.................................

$4,731,930

$

943,148

$3,788,782

\*

In

U.S.

dollars

unless

otherwise

indicated.

See

Note 8 regarding

other

derivative

information.

See

A

bbreviations

on

.

Putnam

Mortgage

Securities

Fund

Financial

Statements

Statement

of

Assets

and

Liabilities

March

31,

2026

(unaudited)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
Assets:

Investments

in

securities:

Cost

-

Unaffiliated

issuers

...................................................................

$1,164,010,197

Cost

-

Non-controlled

affiliates

(Note

g)

........................................................

53,474,576

Value

-

Unaffiliated

issuers

..................................................................

$1,153,289,250

Value

-

Non-controlled

affiliates

(Note

g)

.......................................................

53,474,576

Cash

....................................................................................

4,355,048

Receivables:

Investment

securities

sold

...................................................................

256,000

Receivable

for

sales

of

TBA

securities

(Note

d)

..................................................

250,246,563

Capital

shares

sold

........................................................................

116,215

Dividends

and

interest

.....................................................................

2,975,658

Deposits

with

brokers

for:

Centrally

cleared

swap

contracts

............................................................

12,955,702

Variation

margin

on

futures

contracts

...........................................................

196,329

OTC

swap

contracts

(upfront

payments)

..........................................................

7,141,835

Unrealized

appreciation

on

forward

premium

swap

option

contracts

.....................................

1,847,572

Unrealized

appreciation

on

OTC

swap

contracts

....................................................

632,087

Prepaid

expenses

..........................................................................

307,071

Other

assets

..............................................................................

1,251

Total

assets

..........................................................................

1,487,795,157

Liabilities:

Payables:

Investment

securities

purchased

..............................................................

1,666,962

Payable

for

purchases

of

TBA

securities

(Note

d)

................................................

836,341,289

Capital

shares

redeemed

...................................................................

574,983

Management

fees

.........................................................................

121,029

Administrative

fees

........................................................................

2,106

Distribution

fees

..........................................................................

76,543

Transfer

agent

fees

........................................................................

206,401

Trustees'

fees

and

expenses

.................................................................

374,747

Variation

margin

on

centrally

cleared

swap

contracts

...............................................

496,718

Deposits

from

brokers

for:

OTC

derivative

contracts

..................................................................

4,208,000

OTC

swap

contracts

(upfront

receipts)

...........................................................

1,850,245

Unrealized

depreciation

on

OTC

swap

contracts

....................................................

972,801

Unrealized

depreciation

on

forward

premium

swap

option

contracts

.....................................

4,656,031

TBA

sale

commitments,

at

value

(proceeds

$250,130,742)

(Note

1d)

....................................

250,048,811

Accrued

expenses

and

other

liabilities

...........................................................

97,575

Total

liabilities

.........................................................................

1,101,694,241

Net

assets,

at

value

.................................................................

$386,100,916

Net

assets

consist

of:

Paid-in

capital

.............................................................................

$804,299,339

Total

distributable

earnings

(losses)

.............................................................

(418,198,423)

Net

assets,

at

value

.................................................................

$386,100,916

Putnam

Mortgage

Securities

Fund

Financial

Statements

Statement

of

Assets

and

Liabilities

(continued)

March

31,

2026

(unaudited)

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Class

#### A:
Net

assets,

at

value

.......................................................................

$345,983,931

Shares

outstanding

........................................................................

43,575,000

Net

asset

value

per

share

a,b

..................................................................

$7.94

Maximum

offering

price

per

share

(net

asset

value

per

share

÷

96.00%)

b

................................

$8.27

#### Class

#### C:
Net

assets,

at

value

.......................................................................

$1,536,073

Shares

outstanding

........................................................................

196,472

Net

asset

value

and

maximum

offering

price

per

share

a,b

............................................

$7.82

#### Class

#### R:
Net

assets,

at

value

.......................................................................

$3,289,834

Shares

outstanding

........................................................................

422,496

Net

asset

value

and

maximum

offering

price

per

share

b

.............................................

$7.79

#### Class

#### R6:
Net

assets,

at

value

.......................................................................

$3,507,548

Shares

outstanding

........................................................................

451,076

Net

asset

value

and

maximum

offering

price

per

share

b

.............................................

$7.78

#### Class

#### Y:
Net

assets,

at

value

.......................................................................

$31,783,530

Shares

outstanding

........................................................................

4,088,348

Net

asset

value

and

maximum

offering

price

per

share

b

.............................................

$7.77

a

Redemption

price

is

equal

to

net

asset

value

less

contingent

deferred

sales

charges,

if

applicable.

b

Net

asset

value

per

share

may

not

recalculate

due

to

rounding.

Putnam

Mortgage

Securities

Fund

Financial

Statements

Statement

of

Operations

for

the

six

months

ended

March

31,

2026

(unaudited)

franklintempleton.com

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
Investment

income:

Dividends:

Non-controlled

affiliates

(Note

g)

.............................................................

$950,594

Interest:

Unaffiliated

issuers:

Paydown

gain

(loss)

.....................................................................

(811,283)

Paid

in

cash

a

...........................................................................

11,551,077

Total

investment

income

...................................................................

11,690,388

Expenses:

Management

fees

(Note

a)

...................................................................

720,624

Administrative

fees

(Note

b)

..................................................................

3,712

Distribution

fees:

(Note

3c)

&nbsp;&nbsp;&nbsp;&nbsp;Class

A

................................................................................

441,746

&nbsp;&nbsp;&nbsp;&nbsp;Class

C

................................................................................

7,858

&nbsp;&nbsp;&nbsp;&nbsp;Class

R

................................................................................

8,385

Transfer

agent

fees:

(Note

3e)

&nbsp;&nbsp;&nbsp;&nbsp;Class

A

................................................................................

331,322

&nbsp;&nbsp;&nbsp;&nbsp;Class

C

................................................................................

1,475

&nbsp;&nbsp;&nbsp;&nbsp;Class

R

................................................................................

3,142

&nbsp;&nbsp;&nbsp;&nbsp;Class

R6

...............................................................................

880

&nbsp;&nbsp;&nbsp;&nbsp;Class

Y

................................................................................

28,388

Custodian

fees

............................................................................

5,737

Reports

to

shareholders

fees

..................................................................

34,742

Registration

and

filing

fees

....................................................................

38,092

Professional

fees

...........................................................................

85,946

Trustees'

fees

and

expenses

(Note

3f)

...........................................................

7,391

Other

....................................................................................

6,088

Total

expenses

.........................................................................

1,725,528

Expense

reductions

(Note

4)

...............................................................

(39,985)

Net

expenses

.........................................................................

1,685,543

Net

investment

income

................................................................

10,004,845

Realized

and

unrealized

gains

(losses):

Net

realized

gain

(loss)

from:

Investments:

Unaffiliated

issuers

......................................................................

967,165

Forward

premium

swap

option

contracts

........................................................

(1,091,496)

Futures

contracts

.........................................................................

44,938

TBA

sale

commitments

.....................................................................

(114,939)

Swap

contracts

...........................................................................

(859,182)

Net

realized

gain

(loss)

..................................................................

(1,053,514)

Net

change

in

unrealized

appreciation

(depreciation)

on:

Investments:

Unaffiliated

issuers

......................................................................

(3,437,783)

Translation

of

other

assets

and

liabilities

denominated

in

foreign

currencies

..............................

Forward

premium

swap

option

contracts

........................................................

1,688,461

Futures

contracts

.........................................................................

244,631

TBA

sale

commitments

.....................................................................

81,931

Swap

contracts

...........................................................................

6,419,721

Net

change

in

unrealized

appreciation

(depreciation)

............................................

4,996,983

Net

realized

and

unrealized

gain

(loss)

............................................................

3,943,469

Net

increase

(decrease)

in

net

assets

resulting

from

operations

..........................................

$13,948,314

a

Includes

amortization

of

premium

and

accretion

of

discount.

Putnam

Mortgage

Securities

Fund

Financial

Statements

Statements

of

Changes

in

Net

Assets

franklintempleton.com

Semiannual

Report

The

accompanying

notes

are

an

integral

part

of

these

financial

statements.

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026
(unaudited)

#### Year

#### Ended

#### September

#### 30,

#### 2025
Increase

(decrease)

in

net

assets:

Operations:

Net

investment

income

.................................................

$10,004,845

$24,818,922

Net

realized

gain

(loss)

.................................................

(1,053,514)

1,331,037

Net

change

in

unrealized

appreciation

(depreciation)

...........................

4,996,983

(3,934,546)

Net

increase

(decrease)

in

net

assets

resulting

from

operations

................

13,948,314

22,215,413

Distributions

to

shareholders:

Class

A

.............................................................

(9,946,240)

(53,216,329)

Class

C

.............................................................

(38,946)

(210,556)

Class

R

.............................................................

(92,587)

(532,695)

Class

R6

............................................................

(108,246)

(635,778)

Class

Y

.............................................................

(869,949)

(4,977,662)

Total

distributions

to

shareholders

..........................................

(11,055,968)

(59,573,020)

Capital

share

transactions:

(Note

2)

Class

A

.............................................................

(15,579,908)

1,323,054

Class

C

.............................................................

(126,081)

171,218

Class

R

.............................................................

(22,327)

(493,887)

Class

R6

............................................................

102,685

(116,287)

Class

Y

.............................................................

(9,200,775)

10,317,191

Total

capital

share

transactions

............................................

(24,826,406)

11,201,289

Net

increase

(decrease)

in

net

assets

...................................

(21,934,060)

(26,156,318)

Net

assets:

Beginning

of

period

.....................................................

408,034,976

434,191,294

End

of

period

..........................................................

$386,100,916

$408,034,976

Putnam

Mortgage

Securities

Fund

franklintempleton.com

Semiannual

Report

Notes

to

Financial

Statements

(unaudited)

#### Putnam

#### Mortgage

#### Securities

#### Fund
1. #### Organization

#### and

#### Significant

#### Accounting

#### Policies
Putnam

Mortgage

Securities

Fund (Fund)

is

registered

under

the

Investment

Company

Act

of

1940

(1940

Act)

as

an

open-

end

management

investment

company.

The Fund

follows

the

accounting

and

reporting

guidance

in

Financial

Accounting

Standards

Board

(FASB)

Accounting

Standards

Codification

Topic

946,

Financial

Services

–

Investment

Companies

(ASC

946)

and

applies

the

specialized

accounting

and

reporting

guidance

in

U.S.

Generally

Accepted

Accounting

Principles

(U.S.

GAAP),

including,

but

not

limited

to,

ASC

946. The

Fund

offers

five classes

of

shares:

Class

A,

Class

C,

Class

R,

Class

R6

and

Class

Y. Class

C

shares

automatically

convert

to

Class

A

shares

on

a

monthly

basis,

after

they

have

been

held

for

years.

Each

class

of

shares

may

differ

by

its

initial

sales

load,

contingent

deferred

sales

charges,

voting

rights

on

matters

affecting

a

single

class,

its

exchange

privilege

and

fees

due

to

differing

arrangements

for

distribution

and

transfer

agent

fees.

The

following

summarizes

the Fund's

significant

accounting

policies.

a. #### Financial

#### Instrument

#### Valuation
The

Fund's

investments

in

financial

instruments

are

carried

at

fair

value

daily.

Fair

value

is

the

price

that

would

be

received

to

sell

an

asset

or

paid

to

transfer

a

liability

in

an

orderly

transaction

between

market

participants

on

the

measurement

date.

The

Fund

calculates

the

net

asset

value

(NAV)

per

share

each business

day as

of

p.m.

Eastern

time

or

the

regularly

scheduled

close

of

the

New

York

Stock

Exchange

(NYSE),

whichever

is

earlier.

Under

compliance

policies

and

procedures

approved

by

the Fund's

Board

of

Trustees

(the

Board),

the

Board

has

designated

the

Fund's

investment

manager

as

the

valuation

designee

and

has

responsibility

for

oversight

of

valuation.

The

investment

manager

is

assisted

by

the

Fund's

administrator

in

performing

this

responsibility,

including

leading

the

cross-

functional

Valuation

Committee

(VC).

The

Fund

may

utilize

independent

pricing

services,

quotations

from

securities

and

financial

instrument

dealers,

and

other

market

sources

to

determine

fair

value.

Debt

securities

generally

trade

in

the OTC

market

rather

than

on

a

securities

exchange.

The

Fund's

pricing

services

use

multiple

valuation

techniques

to

determine

fair

value.

In

instances

where

sufficient

market

activity

exists,

the

pricing

services

may

utilize

a

market-based

approach

through

which

quotes

from

market

makers

are

used

to

determine

fair

value.

In

instances

where

sufficient

market

activity

may

not

exist

or

is

limited,

the

pricing

services

also

utilize

proprietary

valuation

models

which

may

consider

market

characteristics

such

as

benchmark

yield

curves,

credit

spreads,

estimated

default

rates,

anticipated

market

interest

rate

volatility,

coupon

rates,

anticipated

timing

of

principal

repayments,

underlying

collateral,

and

other

unique

security

features

in

order

to

estimate

the

relevant

cash

flows,

which

are

then

discounted

to

calculate

the

fair

value.

Investments

in open-end mutual

funds

are

valued

at

the

closing

NAV.

Derivative

financial

instruments

listed

on

an

exchange

are

valued

at

the

official

closing

price

of

the

day.

Certain

derivative

financial

instruments

are

centrally

cleared

or

trade

in

the

OTC

market.

The

Fund's

pricing

services

use

various

techniques

including

industry

standard

option

pricing

models

and

proprietary

discounted

cash

flow

models

to

determine

the

fair

value

of

those

instruments.

The

Fund's

net

benefit

or

obligation

under

the

derivative

contract,

as

measured

by

the

fair

value

of

the

contract,

is

included

in

net

assets.

The

Fund

has

procedures

to

determine

the

fair

value

of

financial

instruments

for

which

market

prices

are

not

reliable

or

readily

available.

Under

these

procedures,

the Fund

primarily

employs

a

market-based

approach

which

may

use

related

or

comparable

assets

or

liabilities,

recent

transactions,

market

multiples,

and

other

relevant

information

for

the

investment

to

determine

the

fair

value

of

the

investment.

An

income-based

valuation

approach

may

also

be

used

in

which

the

anticipated

future

cash

flows

of

the

investment

are

discounted

to

calculate

fair

value.

Discounts

may

also

be

applied

due

to

the

nature

or

duration

of

any

restrictions

on

the

disposition

of

the

investments.

Due

to

the

inherent

uncertainty

of

valuations

of

such

investments,

the

fair

values

may

differ

significantly

from

the

values

that

would

have

been

used

had

an

active

market

existed.

b. #### Foreign

#### Currency

#### Translation
Portfolio

securities

and

other

assets

and

liabilities

denominated

in

foreign

currencies

are

translated

into

U.S.

dollars

based

on

the

exchange

rate

of

such

currencies

against

U.S.

dollars

on

the

date

of

valuation.

The

Fund

may

enter

into

foreign

currency

exchange

contracts

to

facilitate

transactions

denominated

in

a

foreign

currency.

Purchases

and

sales

of

securities,

income

and

expense

items

denominated

in

foreign

currencies

are

translated

into

U.S.

dollars

at

the

exchange

rate

in

effect

on

the

transaction

date.

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

Portfolio

securities

and

assets

and

liabilities

denominated

in

foreign

currencies

contain

risks

that

those

currencies

will

decline

in

value

relative

to

the

U.S.

dollar.

Occasionally,

events

may

impact

the

availability

or

reliability

of

foreign

exchange

rates

used

to

convert

the

U.S.

dollar

equivalent

value.

If

such

an

event

occurs,

the

foreign

exchange

rate

will

be

valued

at

fair

value

using

procedures

established

and

approved

by

the

Board.

The

Fund

does

not

separately

report

the

effect

of

changes

in

foreign

exchange

rates

from

changes

in

market

prices

on

securities

held.

Such

changes

are

included

in

net

realized

and

unrealized

gain

or

loss

from

investments

in

the

Statement of

Operations.

Realized

foreign

exchange

gains

or

losses

arise

from

sales

of

foreign

currencies,

currency

gains

or

losses

realized

between

the

trade

and

settlement

dates

on

securities

transactions

and

the

difference

between

the

recorded

amounts

of

dividends,

interest,

and

foreign

withholding

taxes

and

the

U.S.

dollar

equivalent

of

the

amounts

actually

received

or

paid.

Net

unrealized

foreign

exchange

gains

and

losses

arise

from

changes

in

foreign

exchange

rates

on

foreign

denominated

assets

and

liabilities

other

than

investments

in

securities

held

at

the

end

of

the

reporting

period.

c. #### Stripped

#### Securities
The

Fund

may

invest

in

stripped

securities

which

represent

a

participation

in

securities

that

may

be

structured

in

classes

with

rights

to

receive

different

portions

of

the

interest

and

principal.

Interest-only

securities

receive

all

of

the

interest

and

principal-only

securities

receive

all

of

the

principal.

If

the

interest

only

securities

experience

greater

than

anticipated

prepayments

of

principal,

the

Fund

may

fail

to

recoup

fully

its

initial

investment

in

these

securities.

Conversely,

principal-

only

securities

increase

in

value

if

prepayments

are

greater

than

anticipated

and

decline

if

prepayments

are

slower

than

anticipated.

The

fair

value

of

these

securities

is

highly

sensitive

to

changes

in

interest

rates.

d. #### Purchased

#### on

#### a

#### When-Issued,

#### Forward Commitment or

#### Delayed

#### Delivery

#### Basis

#### and

#### TBA

#### Basis
The

Fund

may

purchase

securities

on

a when-issued,

forward

commitment

or

delayed

delivery

and to-be-

announced

(TBA)

basis,

with

payment

and

delivery

scheduled

for

a

future

date.

These

transactions

are

subject

to

market

fluctuations

and

are

subject

to

the

risk

that

the

value

at

delivery

may

be

more

or

less

than

the

trade

date

purchase

price.

Although

the

Fund

will

generally

purchase

these

securities

with

the

intention

of

holding

the

securities, it

may

sell

the

securities

before

the

settlement

date.

The

Fund

may

also

enter

into

TBA

sale

commitments

to

hedge

its

portfolio

positions,

to

sell

mortgage-backed

securities

it

owns

under

delayed

delivery

arrangements

or

to

take

a

short

position

in

mortgage-backed

securities.

Proceeds

of

TBA

sale

commitments

are

not

received

until

the

contractual

settlement

date.

During

the

time

a

TBA

sale

commitment

is

outstanding,

either

equivalent

deliverable

securities

or

an

offsetting

TBA

purchase

commitment

deliverable

on

or

before

the

sale

commitment

date

are

held

as

"cover"

for

the

transaction,

or

other

liquid

assets

in

an

amount

equal

to

the

notional

value

of

the

TBA

sale

commitment

are

segregated.

If

the

TBA

sale

commitment

is

closed

through

the

acquisition

of

an

offsetting

TBA

purchase

commitment,

the

Fund

realizes

a

gain

or

loss.

If

the

Fund

delivers

securities

under

the

commitment,

the

Fund

realizes

a

gain

or

a

loss

from

the

sale

of

the

securities

based

upon

the

unit

price

established

at

the

date

the

commitment

was

entered

into.

TBA

commitments,

which

are

accounted

for

as

purchase

and

sale

transactions,

may

be

considered

securities

themselves,

and

involve

a

risk

of

loss

due

to

changes

in

the

value

of

the

security

prior

to

the

settlement

date

as

well

as

the

risk

that

the

counterparty

to

the

transaction

will

not

perform

its

obligations.

Counterparty

risk

is

mitigated

by

having

a

master

agreement

between

the

Fund

and

the

counterparty.

Unsettled

TBA

commitments

are

valued

at

their

fair

value

according

to

the

procedures

described

in

the

Financial

Instrument

Valuation

note.

The

contract

is

marked

to

market

daily

and

the

change

in

fair

value

is

recorded

by

the

Fund

as

an

unrealized

gain

or

loss.

Based

on

market

circumstances,

the

investment

manager

will

determine

whether

to

take

delivery

of

the

underlying

securities

or

to

dispose

of

the

TBA

commitments

prior

to

settlement.

1. #### Organization

#### and

#### Significant

#### Accounting

#### Policies
(continued)

b. #### Foreign

#### Currency

#### Translation
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

e. #### Derivative

#### Financial

#### Instruments
The

Fund invested

in

derivative

financial

instruments

in

order

to

manage

risk

or

gain

exposure

to

various

other

investments

or

markets.

Derivatives

are

financial

contracts

based

on

an

underlying

or

notional

amount,

require

no

initial

investment

or

an

initial

net

investment

that

is

smaller

than

would

normally

be

required

to

have

a

similar

response

to

changes

in

market

factors,

and

require

or

permit

net

settlement.

Derivatives

contain

various

risks

including

the

potential

inability

of

the

counterparty

to

fulfill

their

obligations

under

the

terms

of

the

contract,

the

potential

for

an

illiquid

secondary

market,

and/or

the

potential

for

market

movements

which

expose

the

Fund

to

gains

or

losses

in

excess

of

the

amounts

shown

in

the

Statement

of

Assets

and

Liabilities.

Realized

gain

and

loss

and

unrealized

appreciation

and

depreciation

on

these

contracts

for

the

period

are

included

in

the

Statement

of

Operations.

Derivative

counterparty

credit

risk

is

managed

through

a

formal

evaluation

of

the

creditworthiness

of

all

potential

counterparties.

The

Fund

attempts

to

reduce

its

exposure

to

counterparty

credit

risk

on

OTC

derivatives,

whenever

possible,

by

entering

into

International

Swaps

and

Derivatives

Association

(ISDA)

master

agreements

with

certain

counterparties.

These

agreements

contain

various

provisions,

including

but

not

limited

to

collateral

requirements,

events

of

default,

or

early

termination.

Termination

events

applicable

to

the

counterparty

include

certain

deteriorations

in

the

credit

quality

of

the

counterparty.

Termination

events

applicable

to

the

Fund

include

failure

of

the

Fund

to

maintain

certain

net

asset

levels

and/or

limit

the

decline

in

net

assets

over

various

periods

of

time.

In

the

event

of

default

or

early

termination,

the

ISDA

master

agreement

gives

the

non-defaulting

party

the

right

to

net

and

close-out

all

transactions

traded,

whether

or

not

arising

under

the

ISDA

agreement,

to

one

net

amount

payable

by

one

counterparty

to

the

other.

However,

absent

an

event

of

default

or

early

termination,

OTC

derivative

assets

and

liabilities

are

presented

gross

and

not

offset

in

the

Statement

of

Assets

and

Liabilities.

Early

termination

by

the

counterparty

may

result

in

an

immediate

payment

by

the

Fund

of

any

net

liability

owed

to

that

counterparty

under

the

ISDA

agreement.

Collateral

requirements

differ

by

type

of

derivative.

Collateral

or

initial

margin

requirements

are

set

by

the

broker

or

exchange

clearing

house

for

exchange

traded

and

centrally

cleared

derivatives.

Initial

margin

deposited

is

held

at

the

exchange

or

at

the

broker and

can

be

in

the

form

of

cash

and/or

securities.

For

OTC

derivatives

traded

under

an

ISDA

master

agreement,

posting

of

collateral

is

required

by

either

the

Fund

or

the

applicable

counterparty

if

the

total

net

exposure

of

all

OTC

derivatives

with

the

applicable

counterparty

exceeds

the

minimum

transfer

amount,

which

typically

ranges

from

$100,000

to

$250,000,

and

can

vary

depending

on

the

counterparty

and

the

type

of agreement.

Generally,

collateral

is

determined

at

the

close

of

Fund

business

each

day

and

any

additional

collateral

required

due

to

changes

in

derivative

values

may

be

delivered

by

the

Fund

or

the

counterparty

the

next

business

day,

or

within

a

few

business

days.

Collateral

pledged

and/or

received

by

the

Fund

for

OTC

derivatives,

if

any,

is

held

in

segregated

accounts

with

the

Fund's

custodian/counterparty

broker

and

can

be

in

the

form

of

cash

and/or

securities.

Unrestricted

cash

may

be

invested

according

to

the

Fund's

investment

objectives.

To

the

extent

that

the

amounts

due

to

the

Fund

from

its

counterparties

are

not

subject

to

collateralization

or

are

not

fully

collateralized,

the

Fund

bears

the

risk

of

loss

from

counterparty

non-performance.

The

Fund

entered

into

exchange

traded

futures

contracts

primarily

to

manage

and/or

gain

exposure

to

interest

rate

risk.

A

futures

contract

is

an

agreement

between

the

Fund

and

a

counterparty

to

buy

or

sell

an

asset

at

a

specified

price

on

a

future

date.

Required

initial

margins

are

pledged

by

the

Fund,

and

the

daily

change

in

fair

value

is

accounted

for

as

a

variation

margin

payable

or

receivable

in

the

Statement

of

Assets

and

Liabilities.

Futures

contracts

outstanding

at

period

end,

if

any,

are

listed

in

the

Fund's

Schedule

of

Investments.

The

Fund

entered

into

credit

default

swap

contracts

primarily

to

manage

and/or

gain

exposure

to

credit

risk.

A

credit

default

swap

is

an

agreement

between

the

Fund

and

a

counterparty

whereby

the

buyer

of

the

contract

receives

credit

protection

and

the

seller

of

the

contract

guarantees

the

credit

worthiness

of

a

referenced

debt

obligation.

These

agreements

may

be

privately

negotiated

in

the

over-the-

counter

market

(OTC

credit

default

swaps)

or

may

be

executed

in

a

multilateral

trade

facility

platform,

such

as

a

registered

exchange

(centrally

cleared

credit

default

swaps).

The

underlying

referenced

debt

obligation

may

be

a

single

issuer

of

corporate

or

sovereign

debt,

a

credit

1. #### Organization

#### and

#### Significant

#### Accounting

#### Policies
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

index,

a

basket

of

issuers

or

indices,

or

a

tranche

of

a

credit

index

or

basket

of

issuers

or

indices.

In

the

event

of

a

default

of

the

underlying

referenced

debt

obligation,

the

buyer

is

entitled

to

receive

the

notional

amount

of

the

credit

default

swap

contract

from

the

seller

in

exchange

for

the

referenced

debt

obligation,

a

net

settlement

amount

equal

to

the

notional

amount

of

the

credit

default

swap

less

the

recovery

value

of

the

referenced

debt

obligation,

or

other

agreed

upon

amount.

For

centrally

cleared

credit

default

swaps,

required

initial

margins

are

pledged

by

the

Fund,

and

the

daily

change

in

fair

value

is

accounted

for

as

a

variation

margin

payable

or

receivable

in

the

Statement

of

Assets

and

Liabilities.

Over

the

term

of

the

contract,

the

buyer

pays

the

seller

a

periodic

stream

of

payments,

provided

that

no

event

of

default

has

occurred.

Such

periodic

payments

are

accrued

daily

as

an

unrealized

appreciation or

depreciation

until

the

payments

are

made,

at

which

time

they

are

realized.

Upfront

payments

and

receipts

are

reflected

in

the Statement

of

Assets

and

Liabilities

and

represent

compensating

factors

between

stated

terms

of

the

credit

default

swap

agreement

and

prevailing

market

conditions

(credit

spreads

and

other

relevant

factors).

These

upfront

payments

and

receipts

are

amortized

over

the

term

of

the

contract

as

a

realized

gain

or

loss

in

the Statement

of

Operations.

Credit

default

swap

contracts

outstanding

at

period

end,

if

any,

are

listed

in

the

Fund's

Schedule

of

Investments.

The

Fund entered

into

interest

rate

swap

contracts

primarily

to

manage

interest

rate

risk.

An

interest

rate

swap

is

an

agreement

between

the

Fund

and

a

counterparty

to

exchange

cash

flows

based

on

the

difference

between

two

interest

rates,

applied

to

a

notional

amount.

These

agreements

may

be

privately

negotiated

in

the

over-the-

counter

market

(OTC

interest

rate

swaps)

or

may

be

executed

on

a

registered

exchange

(centrally

cleared

interest

rate

swaps).

For

centrally

cleared

interest

rate

swaps,

required

initial

margins

are

pledged

by

the

Fund,

and

the

daily

change

in

fair

value

is

accounted

for

as

a

variation

margin

payable

or

receivable

in

the

Statement

of

Assets

and

Liabilities.

Over

the

term

of

the

contract,

contractually

required

payments

to

be

paid

and

to

be

received

are

accrued

daily

and

recorded

as

unrealized

appreciation

or

depreciation

until

the

payments

are

made,

at

which

time

they

are

realized.

Interest

rate

swap

contracts

outstanding

at

period

end,

if

any,

are

listed

in

the

Fund's

Schedule

of

Investments.

The

Fund

purchased

or

wrote

OTC

option

contracts

primarily

to

manage

and/or

gain exposure

to

interest

rate

risk.

An

option

is

a

contract

entitling

the

holder

to

purchase

or

sell

a

specific

amount

of

shares

or

units

of

an

asset

or

notional

amount

of

a

swap

(swaption),

at

a

specified

price.

When

an

option

is

purchased

or

written,

an

amount

equal

to

the

premium

paid

or

received

is

recorded

as

an

asset

or

liability,

respectively.

Upon

exercise

of

an

option,

the

acquisition

cost

or

sales

proceeds

of

the

underlying

investment

is

adjusted

by

any

premium

received

or

paid.

Upon

expiration

of

an

option,

any

premium

received

or

paid

is

recorded

as

a

realized

gain

or

loss.

Upon

closing

an

option

other

than

through

expiration

or

exercise,

the

difference

between

the

premium

received

or

paid

and

the

cost

to

close

the

position

is

recorded

as

a

realized

gain

or

loss.

Option

contracts

outstanding

at

period

end,

if

any,

are

listed

in

the

Fund's

Schedule

of

Investments.

See

Note

8 regarding

other

derivative

information.

f. #### Income

#### Taxes
It

is the Fund's

policy

to

qualify

as

a

regulated

investment

company

under

the

Internal

Revenue

Code. The Fund

intends

to

distribute

to

shareholders

substantially

all

of

its

taxable

income

and

net

realized

gains

to

relieve

it

from

federal

income

and

excise

taxes.

As

a

result,

no

provision

for

U.S.

federal

income

taxes

is

required.

The Fund

may

recognize

an

income

tax

liability

related

to

its

uncertain

tax

positions

under

U.S.

GAAP

when

the

uncertain

tax

position

has

a

less

than

50%

probability

that

it

will

be

sustained

upon

examination

by

the

tax

authorities

based

on

its

technical

merits.

As

of

March

31,

2026, the Fund

has

determined

that

no

tax

liability

is

required

in

its

financial

statements

related

to

uncertain

tax

positions

for

any

open

tax

years

(or

expected

to

be

taken

in

future

tax

years).

The

Fund's

federal

and

state

income

and

federal

excise

tax

returns

for

the

prior

three

fiscal

years

are

subject

to

examination

by

the

Internal

Revenue

Service

and

state

departments

of

revenue.

1. #### Organization

#### and

#### Significant

#### Accounting

#### Policies
(continued)

e. #### Derivative

#### Financial

#### Instruments
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

g. #### Security

#### Transactions,

#### Investment

#### Income,

#### Expenses

#### and

#### Distributions
Security

transactions

are

accounted

for

on

trade

date.

Realized

gains

and

losses

on

security

transactions

are

determined

on

a

specific

identification

basis.

Interest

income

(including

interest

income

from

payment-in-kind

securities,

if

any)

and

estimated

expenses

are

accrued

daily.

Amortization

of

premium

and

accretion

of

discount

on

debt

securities

are

included

in

interest

income.

Paydown

gains

and

losses

are

recorded

separately

in

the

Statement

of

Operations.

Dividend

income

is

recorded

on

the

ex-dividend

date.

Distributions

to

shareholders

are

recorded

on

the

ex-dividend

date.

Distributable

earnings

are

determined

according

to

income

tax

regulations

(tax

basis)

and

may

differ

from

earnings

recorded

in

accordance

with

U.S.

GAAP.

These

differences

may

be

permanent

or

temporary.

Permanent

differences

are

reclassified

among

capital

accounts

to

reflect

their

tax

character.

These

reclassifications

have

no

impact

on

net

assets

or

the

results

of

operations.

Temporary

differences

are

not

reclassified,

as

they

may

reverse

in

subsequent

periods.

Realized

and

unrealized

gains

and

losses

and

net

investment

income,

excluding

class

specific

expenses,

are

allocated

daily

to

each

class

of

shares

based

upon

the

relative

proportion

of

net

assets

of

each

class.

Differences

in

per

share

distributions

by

class

are

generally

due

to

differences

in

class

specific

expenses.

h. #### Accounting

#### Estimates
The

preparation

of

financial

statements

in

accordance

with

U.S.

GAAP

requires

management

to

make

estimates

and

assumptions

that

affect

the

reported

amounts

of

assets

and

liabilities

at

the

date

of

the

financial

statements

and

the

amounts

of

income

and

expenses

during

the

reporting

period.

Actual

results

could

differ

from

those

estimates.

i. #### Guarantees

#### and

#### Indemnifications
Under

the Fund's

organizational

documents,

its

officers

and trustees

are

indemnified

by

the

Fund against

certain

liabilities

arising

out

of

the

performance

of

their

duties

to

the

Fund.

Additionally,

in

the

normal

course

of

business,

the

Fund

enters

into

contracts

with

service

providers

that

contain

general

indemnification

clauses.

The Fund's

maximum

exposure

under

these

arrangements

is

unknown

as

this

would

involve

future

claims

that

may

be

made

against

the Fund

that

have

not

yet

occurred.

Currently,

the Fund

expects

the

risk

of

loss

to

be

remote.

2. #### Shares

#### of

#### Beneficial

#### Interest
At

March

31,

2026,

there

were

an

unlimited

number

of

shares

authorized

(without

par

value).

Transactions

in

the

Fund's

shares

were

as

follows:

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### Shares

#### Amount

#### Shares

#### Amount

#### Class

#### A

#### Shares:
Shares

sold

a

...................................

610,236

$4,849,274

1,771,074

$14,027,490

Shares

issued

in

reinvestment

of

distributions

..........

1,129,038

8,962,023

6,185,661

47,798,694

Shares

redeemed

...............................

(3,698,736)

(29,391,205)

(7,706,675)

(60,503,130)

Net

increase

(decrease)

..........................

(1,959,462)

$(15,579,908)

250,060

$1,323,054

#### Class

#### C

#### Shares:
Shares

sold

...................................

6,863

$53,807

76,213

$590,089

Shares

issued

in

reinvestment

of

distributions

..........

4,311

33,709

24,557

187,084

Shares

redeemed

a

..............................

(27,259)

(213,597)

(77,385)

(605,955)

Net

increase

(decrease)

..........................

(16,085)

$(126,081)

23,385

$171,218

1. #### Organization

#### and

#### Significant

#### Accounting

#### Policies
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

3. #### Transactions

#### with

#### Affiliates
Franklin

Resources,

Inc.

is

the

holding

company

for

various

subsidiaries

that

together

are

referred

to

as

Franklin

Templeton.

Certain

officers

and trustees

of

the Fund are

also

officers

and/or directors

of

the

following

subsidiaries:

a. #### Management

#### Fees
The

Fund

pays Advisers

a

management

fee

(based

on

the

Fund's

average

net

assets

and

computed

and

paid

monthly)

at

annual

rates

that

may

vary

based

on

the

average

of

the

aggregate

net

assets

of

all

open-end

mutual

funds

sponsored

by

Putnam

Management

(including

open-end

funds

managed

by

affiliates

of

Putnam

Management

that

have

been

deemed

to

#### Six

#### Months

#### Ended

#### March

#### 31,

#### 2026

#### Year

#### Ended

#### September

#### 30,

#### 2025

#### Shares

#### Amount

#### Shares

#### Amount

#### Class

#### R

#### Shares:
Shares

sold

...................................

35,741

$277,904

53,828

$418,444

Shares

issued

in

reinvestment

of

distributions

..........

11,895

92,587

69,788

529,963

Shares

redeemed

...............................

(50,071)

(392,818)

(187,099)

(1,442,294)

Net

increase

(decrease)

..........................

(2,435)

$(22,327)

(63,483)

$(493,887)

#### Class

#### R6

#### Shares:
Shares

sold

...................................

28,252

$220,191

315,036

$2,489,643

Shares

issued

in

reinvestment

of

distributions

..........

12,332

95,839

78,433

594,429

Shares

redeemed

...............................

(27,363)

(213,345)

(424,238)

(3,200,359)

Net

increase

(decrease)

..........................

13,221

$102,685

(30,769)

$(116,287)

#### Class

#### Y

#### Shares:
Shares

sold

...................................

1,095,096

$8,534,731

4,615,623

$35,561,078

Shares

issued

in

reinvestment

of

distributions

..........

86,445

671,696

522,956

3,963,766

Shares

redeemed

...............................

(2,359,291)

(18,407,202)

(3,785,779)

(29,207,653)

Net

increase

(decrease)

..........................

(1,177,750)

$(9,200,775)

1,352,800

$10,317,191

a

May

include

a

portion

of

Class

C

shares

that

were

automatically

converted

to

Class

A. #### Subsidiary

#### Affiliation
Franklin

Advisers,

Inc.

(Advisers)

Investment

manager

Putnam

Investment

Management,

LLC

(Putnam

Management)

Subadvisor

Franklin

Templeton

Investment

Management

Limited

(FTIML)

Subadvisor

Franklin

Templeton

Services,

LLC

(FT

Services)

Administrative

manager

Franklin

Distributors,

LLC

(Distributors)

Principal

underwriter

Putnam

Investor

Services,

Inc.

(PSERV)

Transfer

agent

2. #### Shares

#### of

#### Beneficial

#### Interest
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

be

sponsored

by

Putnam

Management

for

this

purpose)

(excluding

net

assets

of

such

funds

that

are

invested

in,

or

that

are

invested

in

by,

other

such

funds

to

the

extent

necessary

to

avoid

"double

counting"

of

those

assets).

Such

annual

rates

may

vary

as

follows:

For

the

period

ended

March

31,

2026,

the

annualized

gross

effective

investment

management

fee

rate

was 0.368%

of

the

Fund's

average daily

net

assets.

Advisers

retained

Putnam

Management

as

subadvisor

for

the

Fund.

Pursuant

to

the

agreement,

Putnam

Management

provides

certain

advisory

and

related

services

to

the

Fund.

Advisers

pays

a

monthly

fee

to

Putnam

Management

based

on

the

costs

of

Putnam

Management

in

providing

these

services

to

the

Fund,

which

may

include

a

mark-up

not

to

exceed

15%

over

such

costs.

Under

a

subadvisory

agreement,

FTIML

provides

subadvisory

services

to

the

Fund.

The

subadvisory

fee

is

paid by Putnam

Management

based

on

the

average

net

assets

managed

by

FTIML,

and

is

not

an

additional

expense

of

the

Fund.

b. #### Administrative

#### Fees
Under

an

agreement

with

Advisers,

FT

Services

provides

administrative

services

to

the

Fund.

The

fee

is

paid

by Advisers

based

on

the Fund's

average

daily

net

assets,

and

is

not

an

additional

expense

of

the

Fund.

The

Fund

reimburses

Advisers

an

allocated

amount

for

the

compensation

and

related

expenses

of

certain

officers

of

the

Fund

and

their

staff

who

provide

administrative

services

to

the

Fund.

The

aggregate

amount

of

all

such

reimbursements

is

determined

annually

by

the

Trustees.

c. #### Distribution

#### Fees
The

Fund

has

adopted

distribution

plans

(the

Plans)

with

respect

to

the

following

share

classes

pursuant

to

Rule

12b–1

under

the

1940

Act.

The

purpose

of

the

Plans

is

to

compensate

Distributors

for

services

provided

and

expenses

incurred

in

distributing

shares

of

the

Fund.

The

Plans

provide

payments

by

the

Fund

to

Distributors

at

an

annual

rate

of

up

to

the

following

amounts

(Maximum

%)

of

the

average

net

assets

attributable

to

each

class.

The

Trustees

have

approved

payment

by

the

Fund

at

the

following

annual

rate

(Approved

%)

of

the

average

net

assets

attributable

to

each

class.

#### Annualized

#### Fee

#### Rate

#### Net

#### Assets
0.550%

of

the

first

$5

billion,

0.500%

of

the

next

$5

billion,

0.450%

of

the

next

$10

billion,

0.400%

of

the

next

$10

billion,

0.350%

of

the

next

$50

billion,

0.330%

of

the

next

$50

billion,

0.320%

of

the

next

$100

billion

and

0.315%

of

any

excess

thereafter.

#### Maximum

#### %

#### Approved

#### %
Class

A

...................................................................

0.35%

0.25%

Class

C

...................................................................

1.00%

1.00%

Class

R

...................................................................

1.00%

0.50%

3. #### Transactions

#### with

#### Affiliates
(continued)

a. #### Management

#### Fees
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

d. #### Sales

#### Charges/Underwriting

#### Agreements
Front-end

sales

charges

and

contingent

deferred

sales

charges

(CDSC)

do

not

represent

expenses

of

the

Fund.

These

charges

are

deducted

from

the

proceeds

of

sales

of

fund

shares

prior

to

investment

or

from

redemption

proceeds

prior

to

remittance,

as

applicable.

Distributors

has

advised

the

Fund

of

the

following

commission

transactions

related

to

the

sales

and

redemptions

of

the

Fund's

shares

for

the

period:

e. #### Transfer

#### Agent

#### Fees
PSERV,

an

affiliate

of

Putnam

Management,

provides

investor

servicing

agent

functions

to

the

Fund.

PSERV

received

fees

for

investor

servicing

for

Class

A,

Class

C,

Class

R

and

Class

Y shares

that

included

(1) a

per

account

fee

for

each

direct

and

underlying

non-defined

contribution

account

(retail

account)

of

the

Fund;

(2) a

specified

rate

of

the

Fund's

assets

attributable

to

defined

contribution

plan

accounts;

and

(3) a

specified

rate

based

on

the

average

net

assets

in

retail

accounts.

PSERV

has

agreed

that

the

aggregate

investor

servicing

fees

for

each

Fund's

retail

and

defined

contribution

accounts

for

these

share

classes

will

not

exceed

an

annual

rate

of

0.25%

of

the

Fund's

average

assets

attributable

to

such

accounts.

Class R6

shares

paid

a

monthly

fee

based

on

the

average

net

assets

of

Class R6

shares

at

an

annual

rate

of

0.05%.

f. #### Trustee

#### Fees
The

Fund

has

adopted

a

Trustee

Fee

Deferral

Plan

(the

Deferral

Plan)

which

allows

the

Trustees to

defer

the

receipt

of

all

or

a

portion

of

Trustees'

fees

payable

from

July

1,

1995

through

December

31,

2023. The

deferred

fees

remain

invested

in

certain

Putnam

funds

until

distribution

in

accordance

with

the

Deferral

Plan.

The

Fund

has

adopted

an

unfunded

noncontributory

defined

benefit

pension

plan

(the

Pension

Plan)

covering

all

Trustees

of

the

Fund

who

have

served

as

a

Trustee

for

at

least

five

years

and

were

first

elected

prior

to

2004. Benefits

under

the

Pension

Plan

are

equal

to

50%

of

the

Trustee's

average

annual

attendance

and

retainer

fees

for

the

three

years

ended

December

31,

2005. The

retirement

benefit

is

payable

during

a

Trustee's

lifetime,

beginning

the

year

following

retirement,

for

the

number

of

years

of

service

through

December

31,

2006. Pension

expense

for

the

Fund

is

included

in

the

Trustees' fees

and

expenses

in

the

Statement

of

Operations.

Accrued

pension

liability

is

included

in

Payable

for

Trustees' fees

and

expenses

in

the

Statement

of

Assets

and

Liabilities.

The

Trustees

have

terminated

the

Pension

Plan

with

respect

to

any

Trustee

first

elected

after

2003. g. #### Investments

#### in

#### Affiliated

#### Management

#### Investment

#### Companies
The

Fund

invests

in

one

or

more

affiliated

management

investment

companies.

As

defined

in

the

1940

Act,

an

investment

is

deemed

to

be

a

"Controlled

Affiliate"

of

a

fund

when

a

fund

owns,

either

directly

or

indirectly,

25%

or

more

of

the

affiliated

fund's

outstanding

shares

or

has

the

power

to

exercise

control

over

management

or

policies

of

such

fund.

The

Fund

does

not

invest

for

purposes

of

exercising

a

controlling

influence

over

the

management

or

policies.

Management

fees

paid

by

the

Fund

are

waived

on

assets

invested

in

the

affiliated

management

investment

companies,

as

noted

in

the

Statement

of

Operations,

in

an

amount

not

to

exceed

the

management

and

administrative

fees,

if

applicable, paid

directly

or

indirectly

by

each

affiliate.

During

the

period

ended

March

31,

2026,

the

Fund

held

investments

in

affiliated

management

investment

companies

as

follows:

Sales

charges

retained

net

of

commissions

paid

to

unaffiliated

brokers/dealers

..............................

$6,318

CDSC

retained

..............................................................................

$8

3. #### Transactions

#### with

#### Affiliates
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

h. #### Waiver

#### and

#### Expense

#### Reimbursements
Advisers has

contractually

agreed,

through

January

30,

2027,

to

waive

fees

and/or

reimburse

the

Fund's

expenses

to

the

extent

necessary

to

limit

the

cumulative

expenses

of

the

Fund,

exclusive

of

brokerage,

interest,

taxes,

investment-related

expenses,

extraordinary

expenses,

acquired

fund

fees

and

expenses

and

payments

under

the

Fund's

investor

servicing

contract,

investment

management

contract

and

distribution

plans,

on

a

fiscal

year-to-date

basis

to

an

annual

rate

of

0.20%

of

the

Fund's

average

net

assets

over

such

fiscal

year-to-date

period.

Total

expenses

waived

or

paid

are

not

subject

to

recapture

subsequent

to

the

Fund's

fiscal

year

end.

4. #### Expense

#### Offset

#### Arrangement
The Fund has entered

into an

arrangement

with PSERV

whereby

credits

realized

as

a

result

of

uninvested

cash

balances

are

used

to

reduce

a

portion

of

the

Fund's

transfer

agent

fees.

During

the

period

ended

March

31,

2026,

the

fees

were

reduced

as

noted

in

the

Statement

of

Operations.

5. #### Income

#### Taxes
For

tax

purposes,

capital

losses

may

be

carried

over

to

offset

future

capital

gains.

At

September

30,

2025,

the

capital

loss

carryforwards

were

as

follows:

At

March

31,

2026,

the

cost

of

investments

and

net

unrealized

appreciation

(depreciation) for

income

tax

purposes

were

as

follows:

#### &nbsp;&nbsp;&nbsp;&nbsp;aa

#### Value

#### at

#### Beginning

#### of

#### Period

#### Purchases

#### Sales

#### Realized

#### Gain
(Loss)

#### Net

#### Change

#### in

#### Unrealized

#### Appreciation
(Depreciation)

#### Value

#### at

#### End

#### of

#### Period

#### Number

#### of

#### Shares

#### Held

#### at

#### End

#### of

#### Period

#### Investment

#### Income

#### a&nbsp;&nbsp;&nbsp;&nbsp;

#### a

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Non-Controlled

#### Affiliates
Dividends

Putnam

Short

Term

Investment

Fund,

Class

P,

3.821%

......

$48,375,449

$78,578,988

$(73,479,861)

$—

$—

$53,474,576

53,474,576

$950,594

#### Total

#### Affiliated

#### Securities

#### ...
$48,375,449

$78,578,988

$(73,479,861)

$—

$—

$53,474,576

$950,594

Capital

loss

carryforwards

not

subject

to

expiration:

Short

term

................................................................................

$

195,743,808

Long

term

................................................................................

155,860,934

Total

capital

loss

carryforwards

...............................................................

$351,604,742

Cost

of

investments

..........................................................................

$1,029,719,177

Unrealized

appreciation

........................................................................

$30,649,011

Unrealized

depreciation

........................................................................

(96,513,840)

Net

unrealized

appreciation

(depreciation)

..........................................................

$(65,864,829)

3. #### Transactions

#### with

#### Affiliates
(continued)

g. #### Investments

#### in

#### Affiliated

#### Management

#### Investment

#### Companies
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

Differences

between

income

and/or

capital

gains

as

determined

on

a

book

basis

and

a

tax

basis

are

primarily

due

to

differing

treatments

of

defaulted

securities

and

derivative

financial

instruments.

6. #### Investment

#### Transactions
Purchases

and

sales

of

investments (excluding

short

term

securities) for

the

period

ended

March

31,

2026,

aggregated

$4,178,912,706 and

$4,751,987,984,

respectively.

7. #### Credit

#### Risk

#### and

#### Defaulted

#### Securities
At

March

31,

2026,

the

Fund

had 9.6%

of

its

portfolio

invested

in

high

yield

securities

rated

below

investment

grade and

unrated

securities.

These

securities

may

be

more

sensitive

to

economic

conditions

causing

greater

price

volatility

and

are

potentially

subject

to

a

greater

risk

of

loss

due

to

default

than

higher

rated

securities.

The

Fund held

defaulted

securities

and/or

other

securities

for

which

the

income

has

been

deemed

uncollectible.

At

March

31,

2026,

the

aggregate

value

of

these

securities

was $618,610

representing 0.2%

of

the

Fund's

net

assets.

The

Fund

discontinues

accruing

income

on

securities

for

which

income

has

been

deemed

uncollectible

and

provides

an

estimate

for

losses

on

interest

receivable.

The

securities

have

been

identified

in

the

accompanying Schedule

of

Investments.

8. #### Other

#### Derivative

#### Information
At

March

31,

2026,

investments

in

derivative

contracts

are

reflected

in

the Statement of

Assets

and

Liabilities

as

follows:

#### Asset

#### Derivatives

#### Liability

#### Derivatives

#### Derivative

#### Contracts

#### Not

#### Accounted

#### for

#### as

#### Hedging

#### Instruments

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Location

#### Fair

#### Value

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Location

#### Fair

#### Value

#### Putnam

#### Mortgage

#### Securities

#### Fund
Interest

rate

contracts

.......

Variation

margin

on

futures

contracts

$

264,986

a

Variation

margin

on

futures

contracts

$

—

Variation

margin

on

centrally

cleared

swap

contracts

8,247,515

a

Variation

margin

on

centrally

cleared

swap

contracts

4,458,733

a

Unrealized

appreciation

on

forward

premium

swap

option

contracts

1,847,572

Unrealized

depreciation

on

forward

premium

swap

option

contracts

4,656,031

Credit

contracts

............

OTC

swap

contracts

(upfront

payments)

7,141,835

OTC

swap

contracts

(upfront

receipts)

1,850,245

Unrealized

appreciation

on

OTC

swap

contracts

632,087

Unrealized

depreciation

on

OTC

swap

contracts

972,801

Total

....................

$18,133,995

$11,937,810

a

This

amount

reflects

the

cumulative

appreciation

(depreciation)

of

futures

contracts

and

centrally

cleared

swap

contracts

as

reported

in

the

Schedule

of

Investments.

Only

the

variation

margin

receivable/payable

at

period

end

is

separately

reported

within

the

Statement

of

Assets

and

Liabilities.

Prior

variation

margin

movements

were

recorded

to

cash

upon

receipt

or

payment.

5. #### Income

#### Taxes
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

For

the

period

ended

March

31,

2026,

the

effect

of

derivative

contracts

in

the Statement

of

Operations

was

as

follows:

For

the

period

ended

March

31,

2026,

the

average

month

end

notional

amount

of

futures

contracts,

swap

contracts

and

options

represented

$41,372,192,

$1,645,168,886

and

$855,194,500,

respectively.

At

March

31,

2026,

the

Fund's

OTC

derivative

assets

and

liabilities

are

as

follows:

#### Derivative

#### Contracts

#### Not

#### Accounted

#### for

#### as

#### Hedging

#### Instruments

#### Statement

#### of

#### Operations

#### Location

#### Net

#### Realized

#### Gain
(Loss)

#### for

#### the

#### Period

#### Statement

#### of

#### Operations

#### Location

#### Net

#### Change

#### in

#### Unrealized

#### Appreciation
(Depreciation)

#### for

#### the

#### Period

#### Putnam

#### Mortgage

#### Securities

#### Fund
Net

realized

gain

(loss)

from:

Net

change

in

unrealized

&nbsp;&nbsp;&nbsp;&nbsp;appreciation

(depreciation)

on:

Interest

rate

contracts

..........

Futures

contracts

$44,938

Futures

contracts

$244,631

Swap

contracts

(704,477)

Swap

contracts

6,004,416

Forward

premium

swap

option

contracts

(1,091,496)

Forward

premium

swap

option

contracts

1,688,461

Credit

contracts

...............

Swap

contracts

(154,705)

Swap

contracts

415,305

Total

.......................

$(1,905,740)

$8,352,813

#### Gross

#### Amounts

#### of

#### Assets

#### and

#### Liabilities

#### Presented

#### in

#### the

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Assets

#### a

#### Liabilities

#### a

#### Putnam

#### Mortgage

#### Securities

#### Fund
Forward

Premium

Swap

Option

Contracts

...................

$

1,847,572

$

4,656,031

Swap

Contracts

.......................................

7,773,922

2,823,046

Total

.............................................

$9,621,494

$7,479,077

a

Absent

an

event

of

default

or

early

termination,

OTC

derivative

assets

and

liabilities

are

presented

gross

and

not

offset

in

the

Statement

of

Assets

and

Liabilities.

8. #### Other

#### Derivative

#### Information
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

At

March

31,

2026,

OTC

derivative

assets,

which

may

be

offset

against

the

Fund's

OTC

derivative

liabilities

and

collateral

received

from

the

counterparty,

are

as

follows:

#### Amounts

#### Not

#### Offset

#### in

#### the

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Gross

#### Amounts

#### of

#### Assets

#### Presented

#### in

#### the

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Financial

#### Instruments

#### Available

#### for

#### Offset

#### Financial

#### Instruments

#### Collateral

#### Received

#### Cash

#### Collateral

#### Received

#### a

#### Net

#### Amount

#### (Not

#### less

#### than

#### zero)

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Counterparty
BOFA

....................

$

1,832,979

$

(1,832,979)

$

—

$

—

$

—

CITI

.....................

2,730,582

(1,893,363)

—

(837,219)

—

DBAB

...................

—

—

—

—

—

GSCO

...................

2,484,314

(650,282)

—

(1,834,032)

—

JPHQ

...................

369,585

(283,333)

—

—

86,252

MCM

....................

14,593

(14,593)

—

—

—

MLCO

...................

153,303

(153,303)

—

—

—

MSCO

...................

2,036,138

(225,649)

—

(1,508,000)

302,489

NATW

...................

—

—

—

—

—

Total

...................

$9,621,494

$(5,053,502)

$—

$(4,179,251)

$388,741

$

a

In

some

instances,

the

collateral

amounts

disclosed

in

the

table

above

were

adjusted

due

to

the

requirement

to

limit

the

collateral

amounts

to

avoid

the

effect

of

overcollateralization.

Actual

collateral

received

and/or

pledged

may

be

more

than

the

amounts

disclosed

herein.

8. #### Other

#### Derivative

#### Information
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

At

March

31,

2026,

OTC

derivative

liabilities,

which

may

be

offset

against

the

Fund's

OTC

derivative

assets

and

collateral

pledged

to

the

counterparty,

are

as

follows:

See

Note

1(e) regarding

derivative

financial

instruments.

See

Abbreviations

on

.

9. #### Credit

#### Facility
The

Fund,

together

with

other

U.S.

registered

and

foreign

investment

funds

(collectively,

Borrowers),

managed

by

Franklin

Templeton,

are

borrowers

in

a

joint

syndicated

senior

unsecured

credit

facility

totaling

$2.995

billion

(Global

Credit

Facility)

which

matures

on

January

29,

2027. This

Global

Credit

Facility

provides

a

source

of

funds

to

the

Borrowers

for

temporary

and

emergency

purposes,

including

the

ability

to

meet

future

unanticipated

or

unusually

large

redemption

requests.

Under

the

terms

of

the

Global

Credit

Facility,

the

Fund

may,

in

addition

to

interest

charged

on

any

borrowings

made

by

the

Fund

and

other

costs

incurred

by

the

Fund,

pay

its

share

of

fees

and

expenses

incurred

in

connection

with

the

implementation

and

maintenance

of

the

Global

Credit

Facility,

based

upon

its

relative

share

of

the

aggregate

net

assets

of

all

of

the

Borrowers,

including

an

annual

commitment

fee

of

0.15%

based

upon

the

unused

portion

of

the

Global

Credit

Facility.

These

fees

are

reflected

in

other

expenses

in

the

Statement

of

Operations.

During

the

period

ended

March

31,

2026,

the Fund

did

not

use

the

Global

Credit

Facility.

#### Amounts

#### Not

#### Offset

#### in

#### the

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Gross

#### Amounts

#### of

#### Liabilities

#### Presented

#### in

#### the

#### Statement

#### of

#### Assets

#### and

#### Liabilities

#### Financial

#### Instruments

#### Available

#### for

#### Offset

#### Financial

#### Instruments

#### Collateral

#### Pledged

#### a,b

#### Cash

#### Collateral

#### Pledged

#### Net

#### Amount

#### (Not

#### less

#### than

#### zero)

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Counterparty
BOFA

....................

$

3,171,731

$

(1,832,979)

$

(1,116,373)

$

—

$

222,379

CITI

.....................

1,893,363

(1,893,363)

—

—

—

DBAB

...................

489,086

—

(393,924)

—

95,162

GSCO

...................

650,282

(650,282)

—

—

—

JPHQ

...................

283,333

(283,333)

—

—

—

MCM

....................

90,244

(14,593)

(75,651)

—

—

MLCO

...................

469,656

(153,303)

(264,187)

—

52,166

MSCO

...................

225,649

(225,649)

—

—

—

NATW

...................

205,733

—

(205,733)

—

—

Total

...................

$7,479,077

$(5,053,502)

$(2,055,868)

$—

$369,707

a

See

the

accompanying

Schedule

of

Investments

for

securities

pledged

as

collateral

for

derivatives.

b

In

some

instances,

the

collateral

amounts

disclosed

in

the

table

above

were

adjusted

due

to

the

requirement

to

limit

the

collateral

amounts

to

avoid

the

effect

of

overcollateralization.

Actual

collateral

received

and/or

pledged

may

be

more

than

the

amounts

disclosed

herein.

8. #### Other

#### Derivative

#### Information
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

10. #### Fair

#### Value

#### Measurements
The

Fund

follows

a

fair

value

hierarchy

that

distinguishes

between

market

data

obtained

from

independent

sources

(observable

inputs)

and

the Fund's

own

market

assumptions

(unobservable

inputs).

These

inputs

are

used

in

determining

the

value

of

the

Fund's financial

instruments

and

are

summarized

in

the

following

fair

value

hierarchy:

Level

–

quoted

prices

in

active

markets

for

identical

financial

instruments

Level

–

other

significant

observable

inputs

(including

quoted

prices

for

similar

financial

instruments,

interest

rates,

prepayment

speed,

credit

risk,

etc.)

Level

–

significant

unobservable

inputs

(including

the

Fund's

own

assumptions

in

determining

the

fair

value

of

financial

instruments)

The

input

levels

are

not

necessarily

an

indication

of

the

risk

or

liquidity

associated

with

financial

instruments

at

that

level.

A

summary

of

inputs

used

as

of

March

31,

2026,

in

valuing

the

Fund's assets

and

liabilities carried

at

fair

value,

is

as

follows:

11. #### Operating

#### Segments
The Fund operates

as

a

single

operating

segment,

which

is

an

investment

portfolio.

The

portfolio

managers

assigned

to

the

Fund

within

the

Fund's

investment

manager serve

as

the

Chief

Operating

Decision

Maker

("CODM")

and

are

responsible

for

evaluating

the

Fund's

operating

results

and

allocating

resources

in

accordance

with

the

Fund's

investment

strategy.

Internal

reporting

provided

to

the

CODM

aligns

with

the

accounting

policies

and

measurement

principles

used

in

the financial

statements.

#### Level

#### 1

#### Level

#### 2

#### Level

#### 3

#### Total

#### Putnam

#### Mortgage

#### Securities

#### Fund

#### Assets:
Investments

in

Securities:

a

Asset-Backed

Securities

...................

$

—

$

18,503,147

$

—

$

18,503,147

Commercial

Mortgage-Backed

Securities

......

—

101,629,770

—

101,629,770

Mortgage-Backed

Securities

................

—

832,380,849

—

832,380,849

Residential

Mortgage-Backed

Securities

.......

—

64,788,601

—

64,788,601

Agency

Commercial

Mortgage-Backed

Securities

—

125,381,316

—

125,381,316

Short

Term

Investments

...................

53,474,576

10,605,567

—

64,080,143

Total

Investments

in

Securities

...........

$53,474,576

$1,153,289,250

$—

$1,206,763,826

Other

Financial

Instruments:

Forward

Premium

Swap

Option

Contracts

.....

$—

$1,847,572

$—

$1,847,572

Futures

Contracts

.......................

264,986

—

—

264,986

Swap

Contracts

.........................

—

8,879,602

—

8,879,602

Total

Other

Financial

Instruments

.........

$264,986

$10,727,174

$—

$10,992,160

#### Liabilities:
Other

Financial

Instruments:

TBA

Sale

Commitments

...................

$

—

$

250,048,811

$

—

$

250,048,811

Forward

Premium

Swap

Option

Contracts

......

—

4,656,031

—

4,656,031

Swap

Contracts

.........................

—

5,431,534

—

5,431,534

Total

Other

Financial

Instruments

.........

$—

$260,136,376

$—

$260,136,376

a

For

detailed

categories,

see

the

accompanying

Schedule

of

Investments.

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

For

information

regarding

segment

assets,

segment

profit

or

loss,

and

significant

expenses,

refer

to

the Statement

of

Assets

and

Liabilities

and

the Statement

of

Operations,

along

with

the

related

notes

to

the financial

statements.

The Schedule

of

Investments

provides

details

of

the Fund's investments

that

generate

returns

such

as

interest,

dividends,

and

realized

and

unrealized

gains

or

losses.

Performance

metrics,

including

portfolio

turnover

and

expense

ratios,

are

disclosed

in

the Financial

Highlights.

12. #### Subsequent

#### Events
The

Fund

has

evaluated

subsequent

events

through

the

issuance

of

the

financial

statements

and

determined

that

no

events

have

occurred

that

require

disclosure.

11. #### Operating

#### Segments
(continued)

Putnam

Mortgage

Securities

Fund

Notes

to

Financial

Statements

(unaudited)

franklintempleton.com

Semiannual

Report

#### Putnam

#### Mortgage

#### Securities

#### Fund
(continued)

#### Abbreviations

#### Counterparty

#### BOFA
Bank

of

America

NA

#### CITI
Citibank

NA

#### DBAB
Deutsche

Bank

AG

#### GSCO
Goldman

Sachs

Group,

Inc.

#### JPHQ
JPMorgan

Chase

Bank

NA

#### MCM
Mizuho

Capital

Markets

LLC

#### MLCO
Merrill

Lynch

International

&

Co.

#### MSCO
Morgan

Stanley

#### NATW
Natwest

Markets

plc

#### Index

#### CMBX.NA.

#### Series

#### number
CMBX

North

America

Index

#### Selected

#### Portfolio

#### CMT
Constant

Monthly

U.S.

Treasury

Securities

Yield

Curve

Rate

Index

#### FHLMC
Federal

Home

Loan

Mortgage

Corp.

#### FNMA
Federal

National

Mortgage

Association

#### FRN
Floating

Rate

Note

#### GNMA
Government

National

Mortgage

Association

#### IO
Interest

Only

#### MBS
Mortgage-Backed

Security

#### REMIC
Real

Estate

Mortgage

Investment

Conduit

#### SOFR
Secured

Overnight

Financing

Rate

#### STACR
Structured

Agency

Credit

Risk

#### T-Note
Treasury

Note

The

following

reference

rates,

and

their

values

as

of

period

end,

are

used

for

security

descriptions:

#### Reference

#### Index

#### Reference

#### Rate
1-day

SOFR

........................

3.68%

Putnam

Mortgage

Securities

Fund

franklintempleton.com

Semiannual

Report

#### Changes

#### In

#### and

#### Disagreements

#### with

#### Accountants
For

the

period

covered

by

this

report

Not

applicable.

#### Results

#### of

#### Meeting(s)

#### of

#### Shareholders
For

the

period

covered

by

this

report

Not

applicable.

#### Remuneration

#### Paid

#### to

#### Directors,

#### Officers

#### and

#### Others
For

the

period

covered

by

this

report

Refer

to

the

financial

statements

included

herein.

Remuneration

to

officers

is

paid

by

the

Fund's

investment

manager

according

to

the

terms

of

the

agreement.

#### Board

#### Approval

#### of

#### Management

#### and

#### Subadvisory

#### Agreements
For

the

period

covered

by

this

report

Not

applicable.

38913-SFSOI

05/26©

2026

Franklin

Templeton.

All

rights

reserved.

ITEM 8. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS FOR OPEN-END MANAGEMENT INVESTMENT COMPANIES.

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR.

ITEM 9. PROXY DISCLOSURES FOR OPEN-END MANAGEMENT INVESTMENT COMPANIES.

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR.

ITEM 10. REMUNERATION PAID TO DIRECTORS, OFFICERS, AND OTHERS OF OPEN-END MANAGEMENT INVESTMENT COMPANIES.

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR.

ITEM 11. STATEMENT REGARDING BASIS FOR APPROVAL OF INVESTMENT ADVISORY CONTRACT.

The information is disclosed as part of the Financial Statements included in Item 7 of this Form N-CSR, as applicable.

ITEM 12. DISCLOSURE OF PROXY VOTING POLICIES AND PROCEDURES FOR CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable.

ITEM 13. PORTFOLIO MANAGERS OF CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable.

ITEM 14. PURCHASES OF EQUITY SECURITIES BY CLOSED-END MANAGEMENT INVESTMENT COMPANY AND AFFILIATED PURCHASERS.

Not applicable.

---

| | |
|:---|:---|
| ITEM 15. | SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS. |

---

There have been no changes to the procedures by which shareholders may recommend nominees to the Registrant's Board of Trustees that would require disclosure herein.

ITEM 16. CONTROLS AND PROCEDURES.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) The Registrants acknowledge the Staff's comment. In future filings on Form N-CSR,
 the certifications required by Rule 30a-2 and Item 19(a)(3) will include the designations "principal executive officer" and
 "principal financial officer" in the signature blocks, reflecting the capacity in which each signatory executes the certification,
 in conformity with the language of the Rule and Form N-CSR. The Registrants may also include each signatory's actual title with
 respect to the Funds alongside the required designation.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b) During the period covered by this report, the Registrant transitioned to a new third-party
 service provider who performs certain accounting and administrative services for the Registrant that are subject to Franklin Templeton's
 oversight.

ITEM 17. DISCLOSURE OF SECURITIES LENDING ACTIVITIES FOR CLOSED-END MANAGEMENT INVESTMENT COMPANIES.

Not applicable.

ITEM 18. RECOVERY OF ERRONEOUSLY AWARDED COMPENSATION.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) Not applicable.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b) Not applicable.

ITEM 19. EXHIBITS.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) (1) Not applicable.

Exhibit 99.CODE ETH

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[(a) (3) Certifications pursuant to section 302 of the Sarbanes-Oxley Act of 2002 attached hereto.](pmsf-efp24654_ex99cert.htm)

Exhibit 99.CERT

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[(b) Certifications pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 attached hereto.](pmsf-efp24654_ex99906cert.htm)

Exhibit 99.906CERT

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this Report to be signed on its behalf by the undersigned, there unto duly authorized.

**Putnam Mortgage Securities Fund**

---

| | |
|:---|:---|
| By: | /s/ Jonathan S. Horwitz |
|  | Jonathan S. Horwitz |
|  | Principal Executive Officer |
| Date: | May 29, 2026 |

---

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

---

| | |
|:---|:---|
| By: | /s/ Jonathan S. Horwitz |
|  | Jonathan S. Horwitz |
|  | Principal Executive Officer |
| Date: | May 29, 2026 |
| By: | /s/ Jeffrey White |
|  | Jeffrey White |
|  | Principal Financial Officer |
| Date: | May 29, 2026 |

---

## Ex-99.Cert

CERTIFICATIONS PURSUANT TO SECTION 302

EX-99.CERT

**<u>CERTIFICATIONS</u>**

I, Jonathan S. Horwitz, certify that:

&nbsp;&nbsp;&nbsp;&nbsp;1. I
 have reviewed this report on Form N-CSR of **Putnam Mortgage Securities Fund**;

&nbsp;&nbsp;&nbsp;&nbsp;2. Based
 on my knowledge, this report does not contain any untrue statement of a material fact or
 omit to state a material fact necessary to make the statements made, in light of the circumstances
 under which such statements were made, not misleading with respect to the period covered
 by this report;

&nbsp;&nbsp;&nbsp;&nbsp;3. Based
 on my knowledge, the financial statements, and other financial information included in this
 report, fairly present in all material respects the financial condition, results of operations,
 changes in net assets, and cash flows (if the financial statements are required to include
 a statement of cash flows) of the registrant as of, and for, the periods presented in this
 report;

&nbsp;&nbsp;&nbsp;&nbsp;4. The
 registrant's other certifying officers and I are responsible for establishing and maintaining
 disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company
 Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under
 the Investment Company Act of 1940) for the registrant and have:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) Designed
 such disclosure controls and procedures, or caused such disclosure controls and procedures
 to be designed under our supervision, to ensure that material information relating to the
 registrant, including its consolidated subsidiaries, is made known to us by others within
 those entities, particularly during the period in which this report is being prepared;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) Designed
 such internal control over financial reporting, or caused such internal control over financial
 reporting to be designed under our supervision, to provide reasonable assurance regarding
 the reliability of financial reporting and the preparation of financial statements for external
 purposes in accordance with generally accepted accounting principles;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c) Evaluated
 the effectiveness of the registrant's disclosure controls and procedures and presented
 in this report our conclusions about the effectiveness of the disclosure controls and procedures,
 as of a date within 90 days prior to the filing date of this report based on such evaluation;
 and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;d) Disclosed
 in this report any change in the registrant's internal control over financial reporting
 that occurred during the period covered by this report that has materially affected, or is
 reasonably likely to materially affect, the registrant's internal control over financial
 reporting; and

&nbsp;&nbsp;&nbsp;&nbsp;5. The
 registrant's other certifying officers and I have disclosed to the registrant's
 auditors and the audit committee of the registrant's board of directors (or persons
 performing the equivalent functions):

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) All
 significant deficiencies and material weaknesses in the design or operation of internal control
 over financial reporting which are reasonably likely to adversely affect the registrant's
 ability to record, process, summarize, and report financial information; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) Any
 fraud, whether or not material, that involves management or other employees who have a significant
 role in the registrant's internal control over financial reporting.

---

| |
|:---|
| Date: May 29, 2026 |
| /s/ Jonathan S. Horwitz |
| Jonathan S. Horwitz |
| Principal Executive Officer |

---

**<u>CERTIFICATIONS</u>**

I, Jeffrey White, certify that:

&nbsp;&nbsp;&nbsp;&nbsp;1. I
 have reviewed this report on Form N-CSR of **Putnam Mortgage Securities Fund**;

&nbsp;&nbsp;&nbsp;&nbsp;2. Based
 on my knowledge, this report does not contain any untrue statement of a material fact or
 omit to state a material fact necessary to make the statements made, in light of the circumstances
 under which such statements were made, not misleading with respect to the period covered
 by this report;

&nbsp;&nbsp;&nbsp;&nbsp;3. Based
 on my knowledge, the financial information included in this report, and the financial statements
 on which the financial information is based, fairly present in all material respects the
 financial condition, results of operations, changes in net assets, and cash flows (if the
 financial statements are required to include a statement of cash flows) of the registrant
 as of, and for, the periods presented in this report;

&nbsp;&nbsp;&nbsp;&nbsp;4. The
 registrant's other certifying officers and I are responsible for establishing and maintaining
 disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company
 Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under
 the Investment Company Act of 1940) for the registrant and have:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) Designed
 such disclosure controls and procedures, or caused such disclosure controls and procedures
 to be designed under our supervision, to ensure that material information relating to the
 registrant, including its consolidated subsidiaries, is made known to us by others within
 those entities, particularly during the period in which this report is being prepared;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) Designed
 such internal control over financial reporting, or caused such internal control over financial
 reporting to be designed under our supervision, to provide reasonable assurance regarding
 the reliability of financial reporting and the preparation of financial statements for external
 purposes in accordance with generally accepted accounting principles;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;c) Evaluated
 the effectiveness of the registrant's disclosure controls and procedures and presented
 in this report our conclusions about the effectiveness of the disclosure controls and procedures,
 as of a date within 90 days prior to the filing date of this report based on such evaluation;
 and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;d) Disclosed
 in this report any change in the registrant's internal control over financial reporting
 that occurred during the period covered by this report that has materially affected, or is
 reasonably likely to materially affect, the registrant's internal control over financial
 reporting; and

&nbsp;&nbsp;&nbsp;&nbsp;5. The
 registrant's other certifying officers and I have disclosed to the registrant's
 auditors and the audit committee of the registrant's board of directors (or persons
 performing the equivalent functions):

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;a) All
 significant deficiencies and material weaknesses in the design or operation of internal control
 over financial reporting which are reasonably likely to adversely affect the registrant's
 ability to record, process, summarize, and report financial information; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;b) Any
 fraud, whether or not material, that involves management or other employees who have a significant
 role in the registrant's internal control over financial reporting.

---

| |
|:---|
| Date: May 29, 2026 |
| /s/ Jeffrey White |
| Jeffrey White |
| Principal Financial Officer |

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## Exhibit 99.906

CERTIFICATIONS PURSUANT TO SECTION 906

EX-99.906CERT

**CERTIFICATION**

**Jonathan S. Horwitz,** Principal Executive Officer, and **Jeffrey White,** Principal Financial Officer of **Putnam Mortgage Securities Fund** (the "Registrant"), each certify to the best of their knowledge that:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1. The Registrant's periodic report on Form N-CSR for the period ended **March 31, 2026** (the "Form N-CSR") fully complies with the requirements of Section 13(a) or 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2. The information contained in the Form N-CSR fairly presents, in all material respects, the financial condition and results of operations of the Registrant.

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| | |
|:---|:---|
| **Principal Executive Officer** | **Principal Financial Officer** |
| Putnam Mortgage Securities Fund | Putnam Mortgage Securities Fund |
| /s/ Jonathan S. Horwitz | /s/ Jeffrey White |
| Jonathan S. Horwitz | Jeffrey White |
| Date: May 29, 2026 | Date: May 29, 2026 |

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This certification is being furnished to the Securities and Exchange Commission solely pursuant to 18 U.S.C. § 1350 and is not being filed as part of the Form N-CSR with the Commission.