Exhibit 99.1

Certification of Chief Executive Officer and Chief Financial Officer

Pursuant to 18 U.S.C. § 1350, as created by Section 906 of the Sarbanes-Oxley Act of 2002, the undersigned officer of Kilroy Realty Corporation (the “Company”) hereby certifies, to his knowledge, that:

(i) the accompanying Quarterly Report on Form 10-Q of the Company for the quarterly period ended March 31, 2003 (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

(ii) the information contained in the Quarterly Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/    JOHN B. KILROY, JR.

John B. Kilroy, Jr.

President and Chief Executive Officer

Date: May 13, 2003

Pursuant to 18 U.S.C. § 1350, as created by Section 906 of the Sarbanes-Oxley Act of 2002, the undersigned officer of Kilroy Realty Corporation (the “Company”) hereby certifies, to his knowledge, that:

(i) the accompanying Quarterly Report on Form 10-Q of the Company for the quarterly period ended March 31, 2003 (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934, as amended; and

(ii) the information contained in the Quarterly Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/     RICHARD E. MORAN JR.

Richard E. Moran Jr.

Executive Vice President and

Chief Financial Officer

Date: May 13, 2003

Each of the foregoing certifications is being furnished solely pursuant to 18 U.S.C. § 1350, and is not being filed as part of the Report or as a separate disclosure document. Signed originals of these written statements required by Section 906 have been provided to Kilroy Realty Corporation and will be retained by Kilroy Realty Corporation and furnished to the Securities and Exchange Commission or its staff upon request.