UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

September 7, 2011

Date of Report (Date of earliest event reported)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Section 1 – Registrant’s Business and Operations

Item 1.01. Entry into a Material Definitive Agreement.

On September 7, 2011, Commonwealth Edison Company (ComEd) issued an aggregate of $600 million principal amount of its first mortgage bonds, consisting of $250 million of its First Mortgage 1.95% Bonds, Series 111, due September 1, 2016, and $350 million of its First Mortgage 3.40% Bonds, Series 112, due September 1, 2021. See Item 2.03 below for a description of the Bonds and related agreements.

Section 2 – Financial Information

Item 2.03. Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

On September 7, 2011, ComEd issued $250 million of its First Mortgage 1.95% Bonds, Series 111, due September 1, 2016 (Series 111 Bonds), and $350 million of its First Mortgage 3.40% Bonds, Series 112, due September 1, 2021 (Series 112 Bonds and, together with the Series 111 Bonds, the Bonds). The Bonds were issued pursuant to ComEd’s Mortgage dated July 1, 1923, as amended and supplemented by supplemental indentures, including the Supplemental Indenture dated August 1, 1944 (Mortgage) and the Supplemental Indenture dated as of August 22, 2011 (Supplemental Indenture). The Mortgage is a first mortgage on ComEd’s utility plant. The proceeds of the Bonds will be used by ComEd to refinance three series of variable rate tax-exempt bonds and one series of maturing first mortgage bonds, and to fund other general corporate purposes. The Bonds were registered under the Securities Act of 1933, as amended, pursuant to ComEd’s Registration Statement on Form S-3 (Registration No. 333-158920), which was declared effective upon filing with the Securities and Exchange Commission (SEC) on April 30, 2009.

The Series 111 Bonds and Series 112 Bonds carry an interest rate of 1.95% per annum and 3.40% per annum, respectively, which is payable semi-annually on March 1 and September 1, commencing March 1, 2012. The Series 111 Bonds and the Series 112 Bonds are redeemable in whole or in part at ComEd’s option (i) at any time prior to August 1, 2016, with respect to the Series 111 Bonds, or June 1, 2021, with respect to the Series 112 Bonds, at a redemption price equal to the greater of 100% of the principal amount to be redeemed or a “make-whole” redemption price calculated as provided in the Supplemental Indenture, plus accrued and unpaid interest up to but excluding the redemption date, and (ii) on or after August 1, 2016, with respect to the Series 111 Bonds, or June 1, 2021, with respect to the Series 112 Bonds, at a redemption price equal to 100% of the principal amount to be redeemed, plus accrued and unpaid interest up to but excluding the redemption date. A copy of the Supplemental Indenture, which sets forth the terms of the Bonds, is attached hereto as Exhibit 4.1 and is incorporated herein by reference.

In connection with the issuance of the Bonds, Sidley Austin LLP provided ComEd with the legal opinion attached to this Current Report as Exhibit 5.1.

A copy of the Underwriting Agreement dated August 30, 2011 between ComEd and BNP Paribas Securities Corp., U.S. Bancorp Investments, Inc. and Wells Fargo Securities, LLC, as representatives of the several underwriters named therein, is filed as Exhibit 1.1. to this Current Report. BNP Paribas Securities Corp., U.S. Bancorp Investments, Inc., Wells Fargo Securities, LLC, Deutsche Bank Securities Inc., CIBC World Markets Corp. and PNC Capital Markets LLC have banking affiliates who are lending parties in ComEd’s revolving credit facility. Some of the underwriters and their affiliates have engaged in, and may in the future engage in, investment banking and other commercial dealings in the ordinary course of business with ComEd and its affiliates. They have received customary fees and commissions for these transactions.

Section 9 – Financial Statements and Exhibits

Item 9.01. Financial Statements and Exhibits.

The following exhibits are filed herewith and are exhibits to the Registration Statement on Form S-3, Registration No. 333-158920, as noted below:

* * * * *

This Current Report includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks and uncertainties. The factors that could cause actual results to differ materially from these forward-looking statements include those discussed herein as well as those discussed in (1) ComEd’s 2010 Annual Report on Form 10-K in (a) ITEM 1A. Risk Factors, (b) ITEM 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations and (c) ITEM 8. Financial Statements and Supplementary Data: Note 18; (2) ComEd’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2011 in (a) Part II, Other Information, ITEM 1A. Risk Factors, (b) Part 1, Financial Information, ITEM 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations and (c) Part I, Financial Information, ITEM 1. Financial Statements: Note 13; and (3) other factors discussed in filings with the SEC by ComEd. Readers are cautioned not to place undue reliance on these forward-looking statements, which apply only as of the date of this Current Report. ComEd does not undertake any obligation to publicly release any revision to its forward-looking statements to reflect events or circumstances after the date of this Current Report.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, ComEd has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

September 7, 2011

EXHIBIT INDEX