EXHIBIT 32.2 CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350, AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 This certification is provided pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, and accompanies the quarterly report on Form 10-Q for the quarter ended September 30, 2006 (the "Form 10-Q") of Mercantile Bank Corporation (the "Issuer"). I, Charles E. Christmas, Senior Vice President, Chief Financial Officer and Treasurer of the Issuer, certify that: (i) the Form 10-Q fully complies with the requirements of Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m(a) or 78o(d)); and (ii) the information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Issuer. Dated: November 8, 2006 /s/ Charles E. Christmas ---------------------------------------- Charles E. Christmas Senior Vice President, Chief Financial Officer and Treasurer