Exhibit 5.1

                       [LETTERHEAD OF COMCAST CORPORATION]





                                                  January 14, 2000



Comcast Corporation
1500 Market Street
Philadelphia, PA  19102-2148

Ladies and Gentlemen:


        I am Senior Deputy General Counsel and Vice President of Comcast
Corporation, a Pennsylvania corporation (the "Company"). I have acted as counsel
to the Company in connection with the Company's Registration Statement on Form
S-3 (No. 333-92509) (the "Registration Statement") filed with the Securities and
Exchange Commission pursuant to the Securities Act of 1933, as amended, for the
registration of the resale by certain selling shareholders named therein and
their permitted transferees of up to 72,837,586 shares (the "Shares") of Class A
Special Common Stock, $1.00 par value, of the Company.


        I have examined originals or copies, certified or otherwise identified
to my satisfaction, of such documents, corporate records, certificates of public
officials and other instruments as I have deemed necessary for the purposes of
rendering this opinion.

        On the basis of the foregoing, I am of the opinion that:

        1. The Shares have been duly authorized and, assuming the due execution
and delivery of certificates representing the Shares, when issued and delivered
in accordance with the terms of the Agreement and Plan of Merger dated as of
November 16, 1999 among the Company, Comcast LCI Holdings, Inc., Lenfest
Communications, Inc. and the stockholders named therein, the Shares will be
validly issued, fully paid and non-assessable, and the issuance thereof is not
subject to any preemptive or similar right.

        I am a member of the Bar of the Commonwealth of Pennsylvania and the
foregoing opinion is limited to the laws of the Commonwealth of Pennsylvania and
the federal laws of the United States of America.

        I hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. In addition, I consent to the reference to me under the
caption "Legal Matters" in the prospectus contained in the Registration
Statement.

                                     Very truly yours,

                                     /s/ Arthur R. Block
                                     -----------------------------
                                     Arthur R. Block
                                     Senior Deputy General Counsel

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