EXHIBIT 5-1

                               [SABW LETTERHEAD]


                                October 30, 2002


ComEd Financing III
Commonwealth Edison Company
10 South Dearborn Street - 37th Floor
Post Office Box 805379
Chicago, Illinois 60680-5379

                  Re:      Registration Statement on Form S-3

Ladies and Gentlemen:

     We refer to the Registration Statement on Form S-3 (the "Registration
Statement") being filed by Commonwealth Edison Company, an Illinois corporation
(the "Company"), and ComEd Financing III, a statutory trust created under the
laws of the State of Delaware (the "Trust"), with the Securities and Exchange
Commission (the "Commission") under the Securities Act of 1933, as amended (the
"Securities Act"), relating to: (i) first mortgage bonds of the Company (the
"Bonds"); (ii) unsecured notes of the Company (the "Senior Indebtedness"); (iii)
unsecured subordinated debentures of the Company to be issued to the Trust (the
"Subordinated Indebtedness"); (iv) shares of cumulative preference stock,
without par value (the "Preference Stock"), of the Company; and (v) trust
preferred securities (the "Trust Preferred Securities") of the Trust and the
related guarantees (the "Guarantees") by the Company with respect to the
obligations of the Trust on any issue of Trust Preferred Securities, in each
case in amounts, at prices and on terms to be determined at the time of an
offering, which Guarantees will be governed by New York law.

     Unless otherwise specified in the applicable prospectus supplement, the
Bonds will be issued under the Company's Mortgage (the "Mortgage"), dated July
1, 1923, as amended and supplemented, between the Company and Illinois Merchants
Trust Company, as trustee (BNY Midwest Trust Company, as current successor
trustee), and D.G. Donovan, as co-trustee (collectively, the "Bonds Trustees"),
which Mortgage is governed by Illinois law; the Senior Indebtedness will be
issued under the Indenture (the "Senior Indenture"), dated September 1, 1987, as
amended and supplemented, between the Company and Citibank, N.A., as trustee
(the "Senior Trustee"), which Senior Indenture is governed by New York law; and
the Subordinated Indebtedness will be issued under the Indenture (the
"Subordinated Indenture"), dated September 1, 1995, as amended and supplemented,
between the Company and Wilmington Trust Company, as trustee (the "Subordinated
Trustee"), which Subordinated Indenture is governed by New York law. The
Preference Stock will be issued in accordance with the Restated Articles of
Incorporation of the Company and the Illinois Business Corporation Act.

     In rendering the opinions expressed below, we have examined and relied upon
a copy of the Registration Statement and the exhibits filed therewith. We have
also examined originals, or copies of originals certified to our satisfaction,
of such agreements, documents, certificates and statements of government
officials and other instruments, and have examined




Commonwealth Edison Company
October 30, 2002
Page 2


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 this opinion letter.
We have assumed the authenticity of all documents submitted to us as originals,
the genuineness of all signatures, the legal capacity of all persons and the
conformity with the original documents of any copies thereof submitted to us for
examination.

     Based on the foregoing, and subject to the qualifications and limitations
hereinafter set forth, we are of the opinion that:

     1. The Company is duly incorporated and validly existing under the laws of
the State of Illinois.

     2. Each series of Bonds will be legally issued and binding obligations of
the Company (except to the extent enforceability may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium, fraudulent transfer or other
similar laws affecting the enforcement of creditors' rights generally and by the
effect of general principles of equity, regardless of whether considered in a
proceeding in equity or at law) when: (i) the Registration Statement, as finally
amended (including any necessary post-effective amendments), shall have become
effective under the Securities Act; (ii) a supplemental indenture related to
such series of Bonds meeting the requirements of the Mortgage has been duly
executed and delivered by the Company and the Bonds Trustees; (iii) a prospectus
supplement with respect to such series of Bonds shall have been filed with the
Commission in compliance with the Securities Act and the rules and regulations
thereunder; (iv) the Company's Board of Directors or a duly authorized committee
thereof (the "Company Board") shall have duly adopted final resolutions
authorizing the issuance and sale of such series of Bonds as contemplated by the
Registration Statement and the Mortgage; and (v) such series of Bonds shall have
been duly executed and authenticated as provided in the Mortgage and such
resolutions and shall have been duly delivered to the purchasers thereof against
payment of the agreed consideration therefor.

     3. Each series of Senior Indebtedness will be legally issued and binding
obligations of the Company (except to the extent enforceability may be limited
by applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent
transfer or other similar laws affecting the enforcement of creditors' rights
generally and by the effect of general principles of equity, regardless of
whether considered in a proceeding in equity or at law) when: (i) the
Registration Statement, as finally amended (including any necessary
post-effective amendments), shall have become effective under the Securities
Act; (ii) a supplemental indenture related to such series of Senior Indebtedness
meeting the requirements of the Senior Indenture has been duly executed and
delivered by the Company and the Senior Trustee; (iii) a prospectus supplement
with respect to such series of Senior Indebtedness shall have been filed with
the Commission in compliance with the Securities Act and the rules and
regulations thereunder; (iv) the Company Board shall have duly adopted final
resolutions authorizing the issuance and sale of such series of Senior
Indebtedness as contemplated by the Registration Statement and the




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October 30, 2002
Page 3


Senior Indenture; and (v) such series of Senior Indebtedness shall have been
duly executed and authenticated as provided in the Senior Indenture and such
resolutions and shall have been duly delivered to the purchasers thereof against
payment of the agreed consideration therefor.

     4. Each series of Subordinated Indebtedness will be legally issued and
binding obligations of the Company (except to the extent enforceability may be
limited by applicable bankruptcy, insolvency, reorganization, moratorium,
fraudulent transfer or other similar laws affecting the enforcement of
creditors' rights generally and by the effect of general principles of equity,
regardless of whether considered in a proceeding in equity or at law) when: (i)
the Registration Statement, as finally amended (including any necessary
post-effective amendments), shall have become effective under the Securities
Act; (ii) a supplemental indenture related to such series of Subordinated
Indebtedness meeting the requirements of the Subordinated Indenture has been
duly executed and delivered by the Company and the Subordinated Trustee; (iii) a
prospectus supplement with respect to such series of Subordinated Indebtedness
shall have been filed with the Commission in compliance with the Securities Act
and the rules and regulations thereunder; (iv) the Company Board shall have duly
adopted final resolutions authorizing the issuance and sale of such series of
Subordinated Indebtedness as contemplated by the Registration Statement and the
Subordinated Indenture; and (v) such series of Subordinated Indebtedness shall
have been duly executed and authenticated as provided in the Subordinated
Indenture and such resolutions and shall have been delivered to the purchasers
thereof against payment of the agreed consideration therefor.

     5. Each series of Preference Stock covered by the Registration Statement
will be legally issued, fully paid and nonassessable when: (i) the Registration
Statement, as finally amended (including any necessary post-effective
amendments), shall have become effective under the Securities Act; (ii) a
prospectus supplement with respect to the sale of such series of Preference
Stock shall have been filed with the Commission in compliance with the
Securities Act and the rules and regulations thereunder; (iii) the Company Board
shall have duly adopted final resolutions in conformity with the Restated
Articles of Incorporation of the Company establishing the designations,
preferences, rights, qualifications, limitations or restrictions of such series
of Preference Stock and authorizing the issuance and sale of such series of
Preference Stock as contemplated by the Registration Statement; (iv) the Company
shall have filed with the Illinois Secretary of State a Statement of Resolution
Establishing Series with respect to such series of Preference Stock; and (v)
certificates representing such series of Preference Stock shall have been duly
executed, countersigned and registered and duly delivered to the purchasers
thereof against payment of the agreed consideration therefor.

     6. Each Guarantee will constitute the legal and binding obligation of the
Company (except to the extent enforceability may be limited by applicable
bankruptcy, insolvency, reorganization, moratorium, fraudulent transfer or other
similar laws affecting the enforcement of creditors' rights generally and by the
effect of general principles of equity, regardless of whether considered in a
proceeding in equity or at law) when: (i) the Registration




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October 30, 2002
Page 4


Statement, as finally amended (including any necessary post-effect amendments),
shall have become effective under the Securities Act; (ii) a prospectus
supplement with respect to such Guarantee shall have been filed with the
Commission in compliance with the Securities Act and the rules and regulations
thereunder; (iii) the Company Board shall have duly adopted final resolutions
authorizing the terms of such Guarantee; (iv) a Guarantee Agreement between the
Company and Wilmington Trust Company, as guarantee trustee (the "Guarantee
Trustee"), substantially in the form filed as an exhibit to the Registration
Statement, evidencing such Guarantee shall have been qualified under the Trust
Indenture Act of 1939, as amended, and duly executed and delivered by the
Company and the Guarantee Trustee; and (v) the Trust Preferred Securities in
respect of which such Guarantee Agreement shall have been executed and delivered
shall have been duly issued and delivered to the purchasers thereof, as
contemplated in the Registration Statement and such resolutions, against payment
of the agreed consideration therefor.

     For the purposes of this opinion letter, we have assumed that, at the time
of the issuance, sale and delivery of each series of Bonds, each series of
Senior Indebtedness, each series of Subordinated Indebtedness, each series of
Preference Stock or the execution and delivery of each Guarantee Agreement, as
the case may be: (i) the authorization thereof by the Company will not have been
modified or rescinded, and there will not have occurred any change in law
affecting the validity, legally binding character or enforceability thereof;
(ii) in the case of the issue of Bonds, Senior Indebtedness, Subordinated
Indebtedness or a Guarantee, the Mortgage, Senior Indenture, the Subordinated
Indenture or the Guarantee Agreement, as applicable, will not have been modified
or amended; and (iii) the Restated Articles of Incorporation of the Company, as
currently in effect, will not have been modified or amended and will be in full
force and effect. For purposes of this opinion letter, we have further assumed
that each Guarantee will be governed by the laws of the State of New York.

     We note that an opinion letter of Richards, Layton & Finger, P.A., Delaware
counsel to the Company, dated and delivered to you concurrently herewith,
addresses, among other things, the legality of the Trust Preferred Securities
covered by the Registration Statement.

     We do not find it necessary for the purposes of this opinion letter to
cover, and accordingly we express no opinion as to, the application of the
securities or blue sky laws of the various states or the District of Columbia to
the sale of the securities to be registered pursuant to the Registration
Statement.




Commonwealth Edison Company
October 30, 2002
Page 2


     We hereby consent to the filing of this opinion letter as an Exhibit to the
Registration Statement and to all references to our firm included in or made a
part of the Registration Statement.

                                           Very truly yours,



                                           /s/ Sidley Austin Brown & Wood