SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported) September 22, 2006

WASHINGTON REAL ESTATE INVESTMENT TRUST

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (301) 984-9400

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 2.03 Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

On September 22, 2006, Washington Real Estate Investment Trust (“WRIT”) sold an additional $10,000,000 aggregate principal amount of 3.875% Convertible Senior Notes due September 15, 2026 (the “Additional Notes”) pursuant to an Underwriting Agreement dated September 6, 2006, between WRIT and Credit Suisse Securities (USA) LLC (the “Underwriter”). The Additional Notes were issued upon the exercise by the Underwriter of an over-allotment option granted by WRIT. WRIT previously issued $100,000,000 aggregate principal amount of 3.875% Senior Convertible Notes due September 15, 2026 on September 11, 2006 (the “Initial Notes” and, together with the Additional Notes, the “Notes”). The issuance of the Additional Notes brings the total aggregate principal amount of Notes outstanding to $110,000,000.

The Notes were issued pursuant to a Registration Statement on Form S-3 (File No. 333-136921), filed with the Securities and Exchange Commission (the “SEC”) on August 28, 2006, and declared automatically effective on the same date. A Prospectus Supplement dated September 6, 2006 relating to the Notes (the “Prospectus Supplement”) and supplementing the Prospectus dated August 28, 2006 (the “Prospectus”) was filed with the SEC on September 6, 2006 pursuant to Rule 424(b)(5) under the Securities Act of 1933, as amended.

The specific pricing and other terms of the Notes are summarized in WRIT’s Current Report on Form 8-K filed with the SEC on September 12, 2006 (the “Previous 8-K”). The Officers’ Certificate establishing the terms of the Notes was filed as Exhibit 4.2 with the Previous 8-K. A general description of the terms of the Notes is included under the caption “Description of the Notes” in the Prospectus Supplement and under the caption “Description of Debt Securities” in the Prospectus. The form of the Additional Notes is attached to this Current Report on Form 8-K as Exhibit 4.1.

Item 9.01. Financial Statements and Exhibits.

The following exhibit is filed with this report on Form 8-K:

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

September 26, 2006

Exhibit Index