# EDGAR Filing Document

**Accession Number:** 0000742212
**File Stem:** 0001193125-25-324181
**Filing Date:** 2025-12
**Character Count:** 4333
**Document Hash:** b711b940ba54bd6856fc3541fa07c1c0
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-324181.hdr.sgml**: 20251218

**ACCESSION NUMBER**: 0001193125-25-324181

**CONFORMED SUBMISSION TYPE**: 497

**PUBLIC DOCUMENT COUNT**: 1

**FILED AS OF DATE**: 20251218

**DATE AS OF CHANGE**: 20251218

**EFFECTIVENESS DATE**: 20251218

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** NORTHWESTERN MUTUAL SERIES FUND INC
- **CENTRAL INDEX KEY:** 0000742212

**ORGANIZATION NAME:**
- **EIN:** 391603401
- **STATE OF INCORPORATION:** MD
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 497
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 002-89971
- **FILM NUMBER:** 251582123

**BUSINESS ADDRESS:**
- **STREET 1:** 720 E WISCONSIN AVE
- **CITY:** MILWAUKEE
- **STATE:** WI
- **ZIP:** 53202
- **BUSINESS PHONE:** 4142992508

**MAIL ADDRESS:**
- **STREET 1:** 720 EAST WISCONSIN AVE
- **CITY:** MILWAUKEE
- **STATE:** WI
- **ZIP:** 53202

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** NORTHWESTERN MUTUAL VARIABLE LIFE SERIES FUND INC
- **DATE OF NAME CHANGE:** 19940830

## Series and Classes Contracts Data

### Research International Core Portfolio (Series ID: S000018230)

---

|  |  |
|:---|:---|
| Class Name                            | Class ID   |
| Research International Core Portfolio | C000050278 |

---

### Short-Term Bond Portfolio (Series ID: S000018233)

---

|  |  |
|:---|:---|
| Class Name                | Class ID   |
| Short-Term Bond Portfolio | C000050281 |

---

## Series and Classes Contracts Data

### Research International Core Portfolio (Series ID: S000018230)

| Class ID   | Class Name                            | Ticker Symbol   |
|:---|:---|:---|
| C000050278 | Research International Core Portfolio |  |

### Short-Term Bond Portfolio (Series ID: S000018233)

| Class ID   | Class Name                | Ticker Symbol   |
|:---|:---|:---|
| C000050281 | Short-Term Bond Portfolio |  |

**Northwestern Mutual Series Fund, Inc.**

Supplement Dated December 18, 2025 to the <br>Statement of Additional Information Dated May 1, 2025, as previously supplemented

The following information supplements the Statement of Additional Information (the "SAI") for the Northwestern Mutual Series Fund, Inc. (the "Series Fund"). You should read this Supplement together with the SAI.

***<u>Sub-Advisory Fee Update – Research International Core and Short-Term Bond Portfolios</u>***

At a meeting held on December 16, 2025, the Board of Directors of the Series Fund approved changes to the sub-advisory fees relating to the Research International Core Portfolio and the Short-Term Bond Portfolio, effective February 1, 2026 (the "Effective Date"). Accordingly, as of the Effective Date, the sub-section of the SAI titled "**The Sub-Advisers**," under "INVESTMENT ADVISORY AND OTHER SERVICES" is revised as noted below.

The disclosure relating to the sub-advisory fees for Massachusetts Financial Services Company ("MFS<sup>®</sup>") with respect to the Research International Core Portfolio is replaced with the following:

"For services provided for the Research International Core Portfolio, Mason Street Advisors pays MFS a fee at the annual rate of 0.275% on the first $1 billion of the Portfolio's net assets, 0.25% on the next $500 million, and 0.225% on assets in excess of $1.5 billion."

The disclosure relating to the sub-advisory fees for T. Rowe Price Associates, Inc. ("TRPA") with respect to the Short-Term Bond Portfolio is replaced with the following:

"For the services provided for the Short-Term Bond Portfolio, Mason Street Advisors pays TRPA a fee at the annual rate of 0.16% on the first $100 million of the Portfolio's average net assets. The sub-advisory fee is reset to 0.15% of the Portfolio's average net assets at $100 million, reset to 0.125% at $250 million, and reset at 0.115% at $500 million. The sub-advisory fee is 0.10% of the Portfolio's average net assets in excess of $500 million and is reset to 0.10% of the Portfolio's average net assets at $1 billion, reset to 0.095% at $2 billion, and reset to 0.09% at $3 billion. TRPA will provide Mason Street Advisors with a transitional fee credit to eliminate any discontinuity between the tiered fee schedule and the flat fee schedule once assets exceed certain amounts."

**Please retain this Supplement for future reference.**

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