Exhibit 4.1

Exhibit 4.1

AAT

AMERICAN ASSETS TRUST, INC.

INCORPORATED UNDER THE LAWS OF THE STATE OF MARYLAND

This Certifies that

is the owner of

FULLY-PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK, $0.01 PAR VALUE PER SHARE, OF

AMERICAN ASSETS TRUST, INC.

transferable on the books of the Corporation in person or by duly authorized attorney upon surrender of the certificate properly endorsed. This Certificate and the shares represented hereby are issued and shall be held subject to all of the provisions of the Articles of Incorporation, as amended (the “Charter”), and the Bylaws, as amended, of the Corporation (copies of which are on file with the Corporation and the Transfer Agent). This certificate is not valid until countersigned by the Transfer Agent and registered by the Registrar.

Witness the facsimile seal of the Corporation and the facsimile signatures of its duly authorized officers.

Dated:

TREASURER

AMERICAN ASSETS TRUST, INC.

CORPORATE

SEAL

MARYLAND

2010

EXECUTIVE CHAIRMAN

SEE REVERSE FOR IMPORTANT

NOTICE ON TRANSFER RESTRICTIONS

AND OTHER INFORMATION

CUSIP 024013 10 4

COUNTERSIGNED AND REGISTERED:

AMERICAN STOCK TRANSFER & TRUST COMPANY, LLC

(New York, NY)

BY:

TRANSFER AGENT AND REGISTRAR

AUTHORIZED SIGNATURE

ABnote North America

711 ARMSTRONG LANE

COLUMBIA, TENNESSEE 38401

(931) 388-3003

SALES: HOLLY GRONER 931-490-7660

PROOF OF: DECEMBER 28, 2010

AMERICAN ASSETS TRUCT, INC.

WO 2840 FC

OPERATOR: JB

REV 2

PLEASE INITIAL THE APPROPRIATE SELECTION FOR THIS PROOF: OK AS IS OK WITH CHANGES MAKE CHANGES AND SEND ANOTHER PROOF

Colors selected for printing: LOGO PRINTS IN PROCESS COLORS. Intaglio prints in SC-7 dark blue.

COLOR: This proof was printed from a digital file or artwork on a graphics quality, color laser printer. It is a good representation of the color as it will appear on the final product. However, it is not an exact color rendition, and the final printed product may appear slightly different from the proof due to the difference between the dyes and printing ink.

IMPORTANT NOTICE

The Corporation will furnish to any stockholder, on request and without charge, a full statement of the information required by Section 2-211(b) of the Corporations and Associations Article of the Annotated Code of Maryland with respect to the designations and any preferences, conversion and other rights, voting powers, restrictions, limitations as to dividends and other distributions, qualifications, and terms and conditions of redemption of the stock of each class which the Corporation has authority to issue and, if the Corporation is authorized to issue any preferred or special class in series, (i) the differences in the relative rights and preferences between the shares of each series to the extent set, and (ii) the authority of the Board of Directors to set such rights and preferences of subsequent series. The foregoing summary does not purport to be complete and is subject to and qualified in its entirety by reference to the Charter, a copy of which will be sent without charge to each stockholder who so requests. Such request must be made to the Secretary of the Corporation at its principal office or to the Transfer Agent.

The shares represented by this certificate are subject to restrictions on Beneficial and Constructive Ownership and Transfer for the purpose of the Corporation’s maintenance of its status as a Real Estate Investment Trust under the Internal Revenue Code of 1986, as amended (the “Code”). Subject to certain further restrictions and except as expressly provided in the Corporation’s Charter, (i) no Person may Beneficially Own or Constructively Own shares of the Corporation’s Common Stock in excess of 7.275% (in value or number of shares) of the outstanding shares of Common Stock of the Corporation unless such Person is an Excepted Holder (in which case the Excepted Holder Limit shall be applicable); (ii) no Person may Beneficially Own or Constructively Own shares of Capital Stock of the Corporation in excess of 7.275% of the value of the total outstanding shares of Capital Stock of the Corporation, unless such Person is an Excepted Holder (in which case the Excepted Holder Limit shall be applicable); (iii) no Person may Beneficially Own or Constructively Own Capital Stock that would result in the Corporation being “closely held” under Section 856(h) of the Code or otherwise cause the Corporation to fail to qualify as a REIT; and (iv) no Person may Transfer shares of Capital Stock if such Transfer would result in the Capital Stock of the Corporation being owned by fewer than 100 Persons. Any Person who Beneficially Owns or Constructively Owns or attempts to Beneficially Own or Constructively Own shares of Capital Stock which causes or will cause a Person to Beneficially Own or Constructively Own shares of Capital Stock in excess or in violation of the above limitations must immediately notify the Corporation. If any of the restrictions on transfer or ownership set forth in (i) through (iii) above are violated, the shares of Capital Stock represented hereby will be automatically transferred to a Trustee of a Trust for the benefit of one or more Charitable Beneficiaries. In addition, the Corporation may take other actions, including redeeming shares upon the terms and conditions specified by the Board of Directors in its sole and absolute discretion if the Board of Directors determines that ownership or a Transfer or other event may violate the restrictions described above. Furthermore, upon the occurrence of certain events, attempted Transfers in violation of the restrictions described above may be void ab initio. All capitalized terms in this legend have the meanings defined in the Charter of the Corporation, as the same may be amended from time to time, a copy of which, including the restrictions on transfer and ownership, will be furnished to each holder of Capital Stock of the Corporation on request and without charge. Requests for such a copy may be directed to the Secretary of the Corporation at its Principal Office.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

TEN COM – as tenants in common UNIF GIFT MIN ACT– Custodian

TEN ENT – as tenants by the entireties (Cust) (Minor)

JT TEN – as joint tenants with right under Uniform Gifts to Minors of survivorship and not as Act tenants in common

(State)

Additional abbreviations may also be used though not in the above list.

For value received, hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING POSTAL ZIP CODE OF ASSIGNEE

Shares of the common stock represented by the within Certificate, and do hereby irrevocably constitute and appoint

Attorney to transfer the said stock on the books of the within-named Corporation with full power of substitution in the premises.

Dated,

NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE, IN EVERY PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT, OR ANY CHANGE WHATEVER.

SIGNATURE(S) GUARANTEED:

THE SIGNATURE(S) MUST BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.

ABnote North America

711 ARMSTRONG LANE

COLUMBIA, TENNESSEE 38401

(931) 388-3003

SALES: HOLLY GRONER 931-490-7660

PROOF OF: DECEMBER 28, 2010

AMERICAN ASSETS TRUST, INC.

WO 2840 BK

OPERATOR: JB

REV 2

PLEASE INITIAL THE APPROPRIATE SELECTION FOR THIS PROOF: OK AS IS OK WITH CHANGES MAKE CHANGES AND SEND ANOTHER PROOF