Filed electronically with the Securities and Exchange Commission on May 17, 2011

 File No. 002-78122

 File No. 811-03495

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

Post-Effective Amendment No. 51

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940

Amendment No. 47

DWS MONEY MARKET TRUST

 (Exact name of Registrant as Specified in Charter)

345 Park Avenue, New York, NY            10154

(Address of Principal Executive Offices)     (Zip Code)

Registrant’s Telephone Number, including Area Code:  (617) 295-1000

Caroline Pearson

Deutsche Investment Management Americas Inc.

One Beacon Street, Boston MA  02108

(Name and Address of Agent for Service)

Copy to:

David A. Sturms, Esq.

Vedder Price P.C.

222 North LaSalle Street

Chicago, Illinois 60601

It is proposed that this filing will become effective (check appropriate box):

[ x |	Immediately upon filing pursuant to paragraph (b)
|__|	On _____________ pursuant to paragraph (b)
|__|	60 days after filing pursuant to paragraph (a)(1)
|__|	On _____________ pursuant to paragraph (a)(1)
|__|	75 days after filing pursuant to paragraph (a)(2)
|__|	On ____________ pursuant to paragraph (a)(2) of Rule 485
|__|	Pursuant to paragraph (a)(3) of Rule 485
	If appropriate, check the following box:
|__|	This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

This filing relates solely to the following Fund(s), (each) a series of the Registrant:

·   Cash Management Fund — Institutional Shares

·   Cash Reserves Fund Institutional — Institutional Class

·   DWS Money Market Series — Institutional Shares

·   NY Tax Free Money Fund – Investment Class and Tax-Exempt New York Money Market Fund Class

·   Tax Free Money Fund Investment — Premier Shares

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this amendment to its Registration Statement to be signed on its behalf by the undersigned, thereto duly authorized, in the City of New York and the State of New York on the 29th day of April 2011.

DWS MONEY MARKET TRUST

By:  /s/Michael G. Clark

Michael G. Clark*

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to its Registration Statement has been signed below by the following persons in the capacities and on the dates indicated:

SIGNATURE	TITLE		DATE
/s/Michael G. Clark
Michael G. Clark*		President		April 29, 2011
/s/Paul H. Schubert
Paul H. Schubert		Chief Financial Officer and Treasurer		April 29, 2011
/s/John W. Ballantine
John W. Ballantine*		Trustee		April 29, 2011
/s/Henry P. Becton, Jr.
Henry P. Becton, Jr.*		Trustee		April 29, 2011
/s/Dawn-Marie Driscoll
Dawn-Marie Driscoll*		Trustee		April 29, 2011
/s/Keith R. Fox
Keith R. Fox*		Trustee		April 29, 2011
/s/Paul K. Freeman
Paul K. Freeman*		Chairperson and Trustee		April 29, 2011
/s/Kenneth C. Froewiss
Kenneth C. Froewiss*		Trustee		April 29, 2011
/s/Richard J. Herring
Richard J. Herring*		Trustee		April 29, 2011
/s/William McClayton
William McClayton*		Trustee		April 29, 2011
/s/Rebecca W. Rimel
Rebecca W. Rimel*		Trustee		April 29, 2011

SIGNATURE TITLE DATE

/s/William N. Searcy, Jr.
William N. Searcy, Jr.*	Trustee	April 29, 2011
/s/Jean Gleason Stromberg
Jean Gleason Stromberg*	Trustee	April 29, 2011
/s/Robert H. Wadsworth
Robert H. Wadsworth*	Trustee	April 29, 2011

*By:           

/s/Caroline Pearson

Caroline Pearson**

Chief Legal Officer

** Attorney-in-fact pursuant to the powers of attorney that are incorporated herein by reference to Post-Effective Amendment No. 45 to the Registration Statement, as filed on April 29, 2008; and as filed on April 30, 2009 in Post-Effective Amendment No. 46 to the Registration Statement.

SIGNATURES

CASH MANAGEMENT PORTFOLIO has duly caused this amendment to the Registration Statements on Form N-1A of DWS Money Market Trust, on behalf of Cash Management Fund, Cash Reserve Fund Institutional, and DWS Money Market Series, and Cash Reserve Fund, Inc. to be signed on its behalf by the undersigned, thereto duly authorized, in the City of New York and the State of New York on the 29th day of April 2011.

 CASH MANAGEMENT PORTFOLIO

                                                                            By:  /s/Michael G. Clark

                                                                                   Michael G. Clark*

                                                                                 President

*By:      /s/Caroline Pearson

      Caroline Pearson**

Chief Legal Officer

** Attorney-in-fact pursuant to the power of attorney filed in Amendment No. 25 to the Registration Statement for Cash Management Portfolio on April 30, 2009.

EXHIBIT INDEX

Index No.	Description of Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase