Old Second Bancorp (OSBC) 10-K 2008 FY Annual 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 Annual Report of Old Second Bancorp, Inc. (the “Company”) on Form 10-K for the period ending December 31, 2008 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

President and Chief Executive Officer

March 15, 2009

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