EXHIBIT 5.1



                           SIDLEY AUSTIN BROWN & WOOD
                                 BANK ONE PLAZA
                            10 SOUTH DEARBORN STREET
                             CHICAGO, ILLINOIS 60603


                                 March 18, 2002


Exelon Corporation
10 South Dearborn Street - 37th Floor
Chicago, Illinois  60680-5379


Ladies and Gentlemen:

            We refer to the Registration Statement on Form S-3 (the
"Registration Statement") being filed by Exelon Corporation, a Pennsylvania
corporation (the "Company"), with the Securities and Exchange Commission (the
"Commission") under the Securities Act of 1933, as amended (the "Securities
Act"), relating to the registration of 3,500,000 shares of common stock, no par
value (the "New Shares"), of the Company to be issued pursuant to the Exelon
Corporation Dividend Reinvestment and Stock Purchase Plan (the "Plan").

            We are familiar with the Articles of Incorporation and By-laws of
the Company currently in effect and the resolutions adopted to date by the Board
of Directors of the Company relating to the Plan and the Registration Statement.
We also have examined originals, or copies of originals certified or otherwise
identified to our satisfaction, of such records of the Company and other
corporate documents, have examined such questions of law and have satisfied
ourselves as to such matters of fact as we have considered relevant and
necessary as a basis for the opinions set forth herein. We have assumed the
authenticity of all documents submitted to us as originals, the genuineness of
all signatures, the legal capacity of all natural persons and the conformity
with the original documents of any copies thereof submitted to us for our
examination.

            Based on the foregoing, we are of the opinion that each New Share
will be legally issued, fully paid and non-assessable when (i) the Registration
Statement shall have become effective under the Securities Act, (ii) such New
Shares shall have been duly issued pursuant to the authorization of the
Company's Board of Directors and (iii) such New Shares shall have been delivered
to the purchaser thereof against payment of the agreed consideration thereof
determined in accordance with the terms of the Plan.

            We hereby consent to the filing of this opinion letter with the
Commission as Exhibit 5.1 to the Registration Statement. In giving this consent,
we do not thereby admit that we are in the category of persons whose consent is
required under Section 7 of the Securities Act or the rules and regulations of
the Commission.

            The foregoing opinions are limited to the substantive laws of the
Commonwealth of Pennsylvania and the federal laws of the United States of
America. We assume no obligation to supplement this opinion letter if any
applicable law changes after the date hereof or if we become aware of any fact
that might change the opinion expressed herein after the date hereof.

            We do not find it necessary for the purposes of the opinions
expressed in this opinion letter, and accordingly we do not purport to cover
herein, the application of the securities or "Blue Sky" laws of the various
states to the issuance of the New Shares.

                                        Very truly yours,



                                        /s/ SIDLEY AUSTIN BROWN & WOOD