As filed with the U.S. Securities and Exchange Commission on January 11, 2019

Securities Act File No. 33-28844

Investment Company Act File No. 811-5812

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	☒
Pre-Effective Amendment No.
Post-Effective Amendment No. 55	☒

and/or

REGISTRATION STATEMENT

UNDER

THE INVESTMENT COMPANY ACT OF 1940 ☒

Amendment No. 63

Legg Mason Partners Premium Money Market Trust*

(Exact Name of Registrant as Specified in Charter)

620 Eighth Avenue

New York, NY 10018

(Address of Principal Executive Offices) (Zip Code)

Registrant’s Telephone Number, including Area Code: (877) 721-1926

Name and address of agent for service:   ROBERT I. FRENKEL Legg Mason Partners Premium Money Market Trust 100 First Stamford Place Stamford, Connecticut 06902 Copy to:   ROGER P. JOSEPH, ESQ. Morgan, Lewis & Bockius LLP One Federal Street Boston, Massachusetts 02110

Continuous

(Approximate Date of Proposed Offering)

It is proposed that this filing will become effective:

☒ 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.

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 Western Asset Premium Liquid Reserves and Western Asset Premium U.S. Treasury Reserves.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended (the “Securities Act”), and the Investment Company Act of 1940, as amended, the Registrant, LEGG MASON PARTNERS PREMIUM MONEY MARKET TRUST, hereby certifies that it meets all requirements for effectiveness of this Post-Effective Amendment to the Registration Statement pursuant to Rule 485(b) under the Securities Act and has duly caused this Post-Effective Amendment to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Baltimore, State of Maryland on this 11th day of January, 2019.

LEGG MASON PARTNERS PREMIUM MONEY MARKET TRUST, on behalf of its series:

Western Asset Premium Liquid Reserves

Western Asset Premium U.S. Treasury Reserves

By:	/s/ Jane Trust
	Jane Trust
	President and Chief Executive Officer

WITNESS our hands on the date set forth below.

Pursuant to the requirements of the Securities Act, this Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities indicated below on January 11, 2019.

Signature	Title
/s/ Jane Trust Jane Trust	President, Chief Executive Officer and Trustee
/s/ Richard F. Sennett Richard F. Sennett	Principal Financial Officer
/s/ Elliott J. Berv* Elliott J. Berv	Trustee
/s/ Jane F. Dasher* Jane F. Dasher	Trustee
/s/ Mark T. Finn* Mark T. Finn	Trustee
/s/ Stephen R. Gross* Stephen R. Gross	Trustee
/s/ Richard E. Hanson, Jr.* Richard E. Hanson, Jr.	Trustee
/s/ Susan M. Heilbron* Susan M. Heilbron	Trustee

/s/ Susan B. Kerley* Susan B. Kerley	Trustee
/s/ R. Richardson Pettit* R. Richardson Pettit	Trustee

*By: /s/ Jane Trust

Jane Trust

* Attorney-in-Fact, pursuant to Power of Attorney.

SIGNATURES

Master Portfolio Trust has duly caused this Post-Effective Amendment to the Registration Statement on Form N-1A of Legg Mason Partners Premium Money Market Trust to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Baltimore, State of Maryland on this 11th day of January, 2019.

MASTER PORTFOLIO TRUST, on behalf of its series:

Liquid Reserves Portfolio

U.S. Treasury Reserves Portfolio

By:	/s/ Jane Trust
	Jane Trust
	President and Chief Executive Officer

WITNESS our hands on the date set forth below.

This Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities indicated below on January 11, 2019.

Signature	Title
/s/ Jane Trust Jane Trust	President, Chief Executive Officer and Trustee
/s/ Richard F. Sennett Richard F. Sennett	Principal Financial Officer
/s/ Elliott J. Berv* Elliott J. Berv	Trustee
/s/ Jane F. Dasher* Jane F. Dasher	Trustee
/s/ Mark T. Finn* Mark T. Finn	Trustee
/s/ Stephen R. Gross* Stephen R. Gross	Trustee
/s/ Richard E. Hanson, Jr.* Richard E. Hanson, Jr.	Trustee
/s/ Susan M. Heilbron* Susan M. Heilbron	Trustee
/s/ Susan B. Kerley* Susan B. Kerley	Trustee

/s/ R. Richardson Pettit* R. Richardson Pettit	Trustee
*By: /s/ Jane Trust Jane Trust

* Attorney-in-Fact, pursuant to Power of Attorney.

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