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

      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 March 31, 2005 (the "Form
10-Q") of Mercantile Bank Corporation (the "Issuer").

      I, Gerald R. Johnson, Jr., Chairman and Chief Executive Officer 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: May 6, 2005

                                  /s/ Gerald R. Johnson, Jr.
                                  ----------------------------------------------
                                  Gerald R. Johnson, Jr.
                                  Chairman and Chief Executive Officer