Erp Operating LTD Partnership 10-Q 2003 Q1 Quarterly report

Exhibit 99.1

CERTIFICATION PURSUANT TO
18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of ERP Operating Limited Partnership (“ERPOP”) on Form 10-Q for the period ending March 31, 2003 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Bruce W. Duncan, Chief Executive Officer of Equity Residential, general partner of ERPOP, certify, pursuant to 18.U.S.C. § 1350, as adopted pursuant to § 906 of the Sarbanes-Oxley Act of 2002, that, to the best of my knowledge:

(1)The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2)The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of ERPOP.

/s/ Bruce W. Duncan

Bruce W. Duncan

Chief Executive Officer of
Equity Residential

May 13, 2003

A signed original of this written statement required by Section 906 has been provided to ERPOP and will be retained by ERPOP and furnished to the Securities and Exchange Commission or its staff upon request.