Company: NMZ
Filing Date: 2025-09-29
Form Type: N-14 8C
Source: 0001999371-25-014188
Chunk: 0

Company: NUVEEN MUNICIPAL HIGH INCOME OPPORTUNITY FUND
Filing Date: 2025-09-29
Form: N-14 8C
Chunk 0
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<div align='center'>As filed with the Securities and Exchange Commission on September 29, 2025</div>

File No. 333-[___]

<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-14

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

☐ Pre-Effective Amendment No.

☐ Post-Effective Amendment No.

NUVEEN MUNICIPAL HIGH INCOME OPPORTUNITY FUND

(Exact Name of Registrant as Specified in Charter)

333 West Wacker Drive

Chicago, Illinois 60606

(Address of Principal Executive Offices: Number, Street, City, State, Zip Code)

(800) 257-8787

(Area Code and Telephone Number)

Mark L. Winget

Vice President and Secretary

Nuveen Investments

333 West Wacker Drive

Chicago, Illinois 60606

(Name and Address of Agent for Service)

Copies to:</div>

| Deborah              
 Bielicke Eades       
 Vedder               
 Price P.C.           
 222                  
 North LaSalle Street 
 Chicago,             
 Illinois 60601       | Eric                           
 F. Fess                        
 Chapman                        
 and Cutler LLP                 
 320                            
 South Canal Street, 27th Floor 
 Chicago,                       
 Illinois 60606                 |

Approximate Date of Proposed Public Offering: As soon as practicable after the effective date of this Registration Statement.

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

<div align='center'>IMPORTANT NOTICE TO SHAREHOLDERS OF
Nuveen New Jersey Quality Municipal Income Fund (NXJ)
Nuveen Pennsylvania Quality Municipal Income Fund (NQP)
Nuveen Missouri Quality Municipal Income Fund (NOM)
AND
Nuveen Municipal High Income Opportunity Fund (NMZ)
(EACH, A “FUND” AND TOGETHER, THE “FUNDS”)

[•], 2025</div>

Although we recommend that you read the complete Joint Proxy Statement/Prospectus, for your convenience, we have