Exhibit (5)-1
                              Commonwealth Edison Company and ComEd Financing II
                              Form S-4 File No. 333-


                        [Letterhead of Sidley & Austin]


                                  June 3, 1997



The Board of Directors
Commonwealth Edison Company
10 South Dearborn Street - 37th Floor
Post Office Box 767
Chicago, Illinois  60690-0767

          Re:  Commonwealth Edison Company
               Registration Statement on Form S-4
               -----------------------------------

Ladies and Gentlemen:

          We refer to the Registration Statement on Form S-4 (the "Registration
Statement") being filed by Commonwealth Edison Company, an Illinois corporation
(the "Company"), and ComEd Financing II, a special purpose statutory business
trust created under the laws of the State of Delaware (the "Trust"), with the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "Securities Act"), relating to: (i) the exchange offer by the Trust of
$150,000,000 aggregate Liquidation Amount of the 8.50% Series B Capital
Securities (liquidation amount $1,000 per Capital Security) of the Trust (the
"New Capital Securities") for up to $150,000,000 aggregate Liquidation Amount of
the outstanding 8.50% Series A Capital Securities (liquidation amount $1,000 per
Capital Security) of the Trust (the "Old Capital Securities"); (ii) the exchange
by the Company with the Trust of $154,640,000 aggregate principal amount of the
Company's 8.50% Series B Subordinated Deferrable Interest Debentures due January
15, 2027 (the "New Debentures") for $154,640,000 aggregate principal amount of
the Company's outstanding 8.50% Series A Subordinated Deferrable Interest
Debentures due January 15, 2027 (the "Old Debentures"); and (iii) the guarantee
(the "New Guarantee") by the Company of the payment of Distributions on, and
payments on liquidation or redemption of, the New Capital Securities pursuant to
the Capital Securities Guarantee Agreement (the "New Guarantee Agreement") to be
entered into between the Company and Wilmington Trust Company, as Trustee (the
"Guarantee Trustee"), which is to be exchanged for the guarantee (the "Old
Guarantee") by the Company of the payment of the Distributions on, and payments
on liquidation or redemption of, the Old Capital Securities pursuant to the
Capital Securities Guarantee Agreement dated as of January 24, 1997 between the
Company and Wilmington Trust Company, as Trustee. The New Capital Securities are
to be issued under the Amended and Restated Trust Agreement dated as of January
24, 1997 (the "Trust Agreement") among the Company, as Depositor, Wilmington
Trust Company, as Property Trustee, the Administrative Trustees named

S i d l e y  &  A u s t i n                                       C h i c a g o 

  The Board of Directors
  Commonwealth Edison Company
  June 3, 1997
  Page 2


therein and the holders, from time to time, of undivided beneficial interests in
the assets of the Trust.  The New Debentures are to be issued under the
Indenture dated as of September 1, 1995 between the Company and Wilmington Trust
Company, as Debenture Trustee, as supplemented from time to time (collectively,
the "Indenture").  Capitalized terms not defined herein have the meanings
specified in the Registration Statement.

          We have relied, as to various questions of fact material to such
opinions, upon certificates of officers of the Company.  We have also examined
originals, or copies of originals certified to our satisfaction, of such
agreements, documents, certificates and other statements of government officials
and other instruments, 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 such opinions.  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:

          1.  All necessary corporate action has been taken by the Company to
     authorize and issue the New Debentures and the New Guarantee.

          2.  The New Debentures 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 relating to or affecting the enforcement of
     creditors' rights generally and by the effect of general principles of
     equity, regardless of whether enforceability is considered in a proceeding
     in equity or at law) when (i) the Registration Statement, as finally
     amended, shall have become effective under the Securities Act and the
     Indenture shall have been qualified under the Trust Indenture Act of 1939,
     as amended (the "Trust Indenture Act"), and (ii) the New Debentures shall
     have been duly executed and authenticated as provided in the Indenture and
     shall have been duly delivered against surrender and cancellation of a like
     principal amount of the Old Debentures in the manner described in the
     Registration Statement.

          3.  The New Guarantee will be a legally issued 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 relating to or affecting the enforcement of
     creditors' rights generally and by the effect of general principles of
     equity, regardless of whether

S i d l e y  &  A u s t i n                                       C h i c a g o 

  The Board of Directors
  Commonwealth Edison Company
  June 3, 1997
  Page 3

 
     enforceability is considered in a proceeding in equity or at law) when (i)
     the Registration Statement, as finally amended, shall have become effective
     under the Securities Act and the New Guarantee Agreement shall have been
     qualified under the Trust Indenture Act and (ii) the New Guarantee
     Agreement shall have been duly executed and delivered by the Company and
     the Guarantee Trustee.

          The opinions expressed above are limited to the laws of the States of
New York and Illinois and the federal laws of the United States of America.

          We do not find it necessary for the purposes of this opinion to cover,
and accordingly we express no opinion as to, the application of the securities
or blue sky laws of the various states to the issuance of the New Debentures in
exchange for the Old Debentures or to the issuance of the New Guarantee in
exchange for the Old Guarantee.

          We hereby consent to the filing of this opinion 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,

                                    Sidley & Austin