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                                                                    EXHIBIT 10.3

                             Amendment Number One
                                      To
                           Stock Purchase Agreement


     This Amendment Number One (this "Amendment") is made as of
February 28, 2000, between RCN Corporation, a Delaware corporation
(the "Corporation"), and Vulcan Ventures Incorporated, a Washington
corporation ("Buyer"), to the Stock Purchase Agreement between the
Corporation and Buyer dated as of October 1, 1999 (the "Stock Purchase
Agreement"). Capitalized terms used herein and not otherwise defined
herein shall have the meanings ascribed to such terms as set forth in
the Stock Purchase Agreement.

     WHEREAS, the Corporation and Buyer desire to amend certain provisions of
the Stock Purchase Agreement, as set forth below.

     NOW, THEREFORE, the parties hereto agree as follows:

1.   Amendment.  Section 6.05 of the Stock Purchase Agreement is
     hereby amended and restated in its entirety as follows:

     "Section 6.05. Voting Arrangements. During the Standstill Period,
     Buyer shall vote and cause to be voted all Voting Securities
     owned by the Buyer (i) for nominees to the Board of Directors of
     the Corporation who have been recommended by the Corporation's
     Board of Directors and (ii) on all other matters submitted to the
     holders of Voting Securities, either in accordance with the
     recommendations of the Corporation's Board of Directors or in
     proportion to the votes cast by the other holders of Voting
     Securities; provided that (A) with respect to any Takeover
     Proposal submitted to the vote of the Corporation's stockholders,
     Buyer shall be free to vote without restriction all Voting
     Securities beneficially owned by it and (B) with respect to any
     proposal to approve the issuance of equity securities by the
     Corporation (not including a proposal to approve a stock option
     or other director or officer compensation plan and not in
     connection with a Takeover Proposal) (a "Stock Issuance
     Proposal") submitted to the vote of the Corporation's
     stockholders, Buyer shall be free to vote without restriction
     Voting Securities beneficially owned by it representing up to the
     Agreed Percentage (disregarding clause (i) of the proviso in the
     definition of such term) of the Total Voting Power. Buyer shall
     cause all Voting Securities owned by Buyer to be represented, in
     person or by proxy, at all meetings of holders of Voting
     Securities of which Buyer has actual notice, so that such Voting
     Securities may be counted for the purpose of determining the
     presence of a quorum at such meetings. The
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     Corporation agrees to give Buyer reasonable advance notice of the
     record date of any meeting of stockholders (or consent
     solicitation) to which a Takeover Proposal or a Stock Issuance
     Proposal will be submitted for approval (or in respect of which
     consents will be sought) so that Buyer may, subject to the other
     provisions of this Agreement, convert shares of Preferred Stock
     into Common Stock prior to the applicable record date and vote
     such shares of Common Stock at such meeting (or execute such
     consent) as permitted hereby. Notwithstanding the foregoing, if
     Buyer's covenant to vote and cause to be voted all Voting
     Securities owned by the Buyer for nominees to the Board of
     Directors who have been recommended by the Corporation's Board of
     Directors is unenforceable, then Buyer shall vote and cause to be
     voted all Voting Securities owned by Buyer for nominees to the
     Board of Directors of the Corporation, at Buyer's election,
     either for the nominees to the Board of Directors of the
     Corporation who have been recommended by the Corporation's Board
     of Directors or in proportion to the votes cast by the other
     holders of Voting Securities.

2.   Effect on Stock Purchase Agreement. Except to the extent of the
     amendment set forth specifically herein, all provisions of the
     Stock Purchase Agreement are and shall remain in full force and
     effect, and the execution, delivery and performance of this
     Amendment shall not operate as a waiver or amendment of any
     provision of the Stock Purchase Agreement not specifically
     amended herein.

3.   Execution in Counterparts; Effectiveness. This Amendment may be
     signed in any number of counterparts, each of which shall be an
     original, with the same effect as if the signatures thereto and
     hereto were upon the same instrument. This Amendment shall become
     effective when each party hereto shall have received a
     counterpart hereof signed by the other party hereto.

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     IN WITNESS WHEREOF, the parties hereto have caused this Amendment
to be duly executed by their respective authorized officers as of the
day and year first above written.


                                   RCN CORPORATION



                                   By: /s/ Timothy J. Stoklosa
                                      -------------------------------------
                                      Name:  Timothy J. Stoklosa
                                      Title: Chief Financial Officer and
                                             Executive Vice President


                                   VULCAN VENTURES
                                   INCORPORATED



                                   By: /s/ William D. Savoy
                                      -------------------------------------
                                      Name:  William D. Savoy
                                      Title: Vice President

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