Old Second Bancorp (OSBC) 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 Old Second Bancorp, Inc. (the “Company”) 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, 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

Chief Executive Officer

May 15, 2003

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