Exhibit 32.1

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 Costco Wholesale Corporation (the “Company”) on Form 10-Q for the quarter ended May 12, 2013, as filed with the Securities and Exchange Commission (the “Report”), I, W. Craig Jelinek , President and Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

(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 the Company.

/S/    W. CRAIG JELINEK	Date: June 11, 2013
W. Craig Jelinek President and Chief Executive Officer

A signed original of this written statement has been provided to and will be retained by Costco Wholesale Corporation and furnished to the Securities and Exchange Commission or its staff upon request.

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 Costco Wholesale Corporation (the “Company”) on Form 10-Q for the quarter ended May 12, 2013, as filed with the Securities and Exchange Commission (the “Report”), I, Richard A. Galanti, Chief Financial Officer of the Company, certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

(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 the Company.

/S/    RICHARD A. GALANTI	Date: June 11, 2013
Richard A. Galanti Executive Vice President and Chief Financial Officer

A signed original of this written statement has been provided to and will be retained by Costco Wholesale Corporation and furnished to the Securities and Exchange Commission or its staff upon request.