Old Second Bancorp (OSBC) 10-Q 2006 Q3 Quarterly report

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 Old Second Bancorp, Inc. (the “Company”) on Form 10-Q for the period ending September 30, 2006 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, William B Skoglund, Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. § 1350, as adopted pursuant to § 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 result of operations of the Company.

/s/ William B. Skoglund

William B. Skoglund

Chairman of the Board, Director

President and Chief Executive Officer
(principal executive officer)

November 8, 2006