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                                                                     EXHIBIT 5.1

                                 BAKER & DANIELS
                                    EST. 1863

     300 NORTH MERIDIAN STREET, SUITE 2700 INDIANAPOLIS, INDIANA 46204-1782
         (317) 237-0300 FAX (317) 237-1000 www.bakerdaniels.com


                                                             INDIANAPOLIS
                                                             FORT WAYNE
                                                             SOUTH BEND
                                                             ELKHART
                                                             WASHINGTON, D.C.
                                                             QINDAO, P.R. CHINA




May 9, 2001


Simon Property Group, Inc.
National City Center
115 West Washington Street, Suite 15 East
Indianapolis, Indiana 46204

Ladies and Gentlemen:

         We have acted as counsel to Simon Property Group, Inc., a Delaware
corporation (the "Company"), in connection with the proposed merger (the
"Merger") of SPG Properties, Inc., a Maryland corporation ("Properties"), with
and into the Company, pursuant to the Agreement of Merger, dated as of May 8,
2001 between the Company and Properties (the "Merger Agreement"). This opinion
is being furnished in connection with the information statement-prospectus (the
"Information Statement-Prospectus") which is included in the Registration
Statement on Form S-4 of the Company (the "Registration Statement") filed on the
date hereof with the Securities and Exchange Commission (the "Commission") under
the Securities Act of 1933, as amended (the "Securities Act"), and in accordance
with the requirements of Item 601(b)(8) of Regulation S-K under the Securities
Act.

         Pursuant to the Registration Statement, 8,000,000 shares of the
Company's 8-3/4% Series F Cumulative Redeemable Preferred Stock, $.0001 par
value, and 3,000,000 shares of the Company's 7.89% Series G Cumulative Step-Up
Premium Rate Preferred Stock, $.0001 par value (collectively, the "Preferred
Shares"), have been registered under the Securities Act for issuance in the
Merger.

         In so acting, we have examined copies of such records of the Company
and such other certificates and documents as we have deemed relevant and
necessary for the opinions hereinafter set forth. In such examination, we have
assumed the genuineness of all signatures, and the authenticity of all documents
submitted to us as originals and the conformity to authentic originals of all
documents submitted to us as certified or reproduced copies. We have also
assumed the legal capacity of all persons executing such documents and the truth
and correctness of any representations or warranties therein contained. As to
various questions of fact material

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Simon Property Group, Inc.              -2-                    May 9, 2001


to such opinions, we have relied upon certificates of officers of the Company
and of public officials. Based upon the foregoing, we are of the opinion that:

     1.   The Company is validly existing and in good standing under the laws of
          the State of Delaware.

     2.   The issuance of the Preferred Shares as contemplated in the
          Registration Statement has been duly authorized by the Company.

     3.   The Preferred Shares, when issued in accordance with the Merger
          Agreement, will be validly issued, fully paid and nonassessable.

         This opinion is limited to the General Corporation Act of the State of
Delaware and the federal laws of the United States of the type typically
applicable to transactions contemplated by the Merger, and we do not express any
opinion with respect to the laws of any other country, state or jurisdiction.

         This opinion letter is limited to the matters stated herein and no
opinion is implied or may be inferred beyond the matters expressly stated. This
opinion letter speaks only as of the date hereof and is limited to present
statutes, regulations and administrative and judicial interpretations. We
undertake no responsibility to update or supplement this opinion letter after
the date hereof.

         We hereby consent to the filing of this letter as an exhibit to the
Registration Statement and to the reference to us in the Information
Statement-Prospectus included as part of the Registration Statement. In giving
such consents, we do not hereby admit that we are in the category of persons
whose consent is required under Section 7 of the Securities Act.

                                                     Very truly yours,


                                                     /s/ Baker & Daniels
                                                     --------------------------
                                                     Baker & Daniels
