UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 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): July 12, 2010

ERP OPERATING LIMITED PARTNERSHIP

(Exact Name of Registrant as Specified in its Charter)

Registrant’s telephone number, including area code: (312) 474-1300

Not applicable

(Former Name or Former Address, if Changed Since Last Report)

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 (see General Instruction A.2. below):

Item 8.01. Other Events.

On July 12, 2010, ERP Operating Limited Partnership, an Illinois limited partnership (the “Company”), agreed to issue $600,000,000 aggregate principal amount of 4.75% Notes due July 15, 2020 (the “Notes”) in a public offering. The Company agreed to sell the Notes pursuant to a Terms Agreement, dated as of July 12, 2010, among the Company and each of Citigroup Global Markets Inc., Deutsche Bank Securities Inc. and Morgan Stanley & Co. Incorporated, as representatives of the underwriters named therein. The Notes will be issued pursuant to an Indenture, dated as of October 1, 1994, between the Company and The Bank of New York Mellon Trust Company, National Association (formerly known as The Bank of New York Trust Company, N.A.) (as successor in interest to J.P. Morgan Trust Company, National Association, as successor in interest to Bank One Trust Company, N.A., successor to The First National Bank of Chicago) (the “Trustee”), as supplemented by the First Supplemental Indenture, dated as of September 9, 2004, by and between the Company and the Trustee, as further supplemented by that certain Second Supplemental Indenture, dated as of August 23, 2006, by and between the Company and the Trustee, and as further supplemented by that certain Third Supplemental Indenture, dated as of June 4, 2007, by and between the Company and the Trustee.

Item 9.01. Financial Statements and Exhibits.

2

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.

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