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                                                                       EXHIBIT 5



                              DICKINSON WRIGHT PLLC
                               500 WOODWARD AVENUE
                                   SUITE 4000
                             DETROIT, MICHIGAN 48226
                               TEL: (313) 223-3500
                            FACSIMILE: (313) 223-3598


August 2, 2001

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

                  RE:      MERCANTILE BANK CORPORATION
                           REGISTRATION STATEMENT ON FORM S-2

Ladies and Gentlemen:

         We are acting as counsel to Mercantile Bank Corporation, a Michigan
corporation (the "Company") in connection with the proposed issuance and sale by
the Company of shares of its common stock ("Common Stock"). The Common Stock is
described in a registration statement on Form S-2 (the "Registration Statement")
filed by the Company with the Securities and Exchange Commission (the
"Commission") under Rule 462 (b) of the Securities Act of 1933, as amended.
The Registration Statement incorporates by reference the contents of the
Company's Registration Statement on Form S-2 (Registration No. 333-65144)
declared effective by the Commission on Wednesday, August 1, 2001.

         In connection with this opinion, we have examined originals, or copies,
certified or otherwise identified to our satisfaction, of the Registration
Statement, the Articles of Incorporation and the By-Laws of the Company, as well
as such other corporate records, documents and other papers as we deemed
necessary to examine for purposes of this opinion. We have assumed the
authenticity, accuracy and completeness of all documents submitted to us as
originals, the conformity to authentic original documents of all documents
submitted to us as certified, conformed or photostatic copies and the
genuineness of all signatures.

         Based on the foregoing, we are of the opinion that the Common Stock,
when issued and sold by the Company as contemplated by the Registration
Statement, will be legally issued, fully paid and non-assessable.

         Our opinion expressed above is limited to the Federal securities laws
and the laws of the State of Michigan currently in effect.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and to the use of our name under the heading "Legal Matters" in the
prospectus included in the Registration Statement.

                                            Very truly yours,


                                            /s/ Dickinson Wright PLLC