<PAGE>   1


                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   FORM 10-Q


(Mark One)
[X]  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
        EXCHANGE ACT OF 1934

For the quarterly period ended June 30, 1999

                                       or

[   ]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
        EXCHANGE ACT OF 1934


                        COMMISSION FILE NUMBER: 1-12473


                             ENRON CAPITAL TRUST I
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                 Delaware                                   76-0518948
      (STATE OR OTHER JURISDICTION OF                    (I.R.S. EMPLOYER
      INCORPORATION OR ORGANIZATION)                    IDENTIFICATION NO.)


                   Enron Bldg.
                1400 Smith Street
                 Houston, Texas                               77002

   (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                (ZIP CODE)

                                 (713) 853-6161
              (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)


       Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.

                   [X] Yes                    [   ] No

       As of June 30, 1999, the Registrant had an aggregate of 8,000,000
8.30% Trust  Preferred  Securities and 247,440 8.30% Trust Common Securities
outstanding.


                               Page 1 of 6 Pages
<PAGE>   2




                             ENRON CAPITAL TRUST I

                                   FORM 10-Q

                                     INDEX

                                                                       Page No.
                                                                       --------
PART I  -  FINANCIAL INFORMATION

ITEM 1.     Financial Statements (see Note below)                          3

ITEM 2.     Management's Discussion and Analysis of Financial
            Conditionand Results of Operations (see Note below)            3


PART II  -  OTHER INFORMATION

ITEM 1.     Legal Proceedings                                              4

ITEM 2.     Changes in Securities                                          4

ITEM 3.     Defaults upon Senior Securities                                4

ITEM 4.     Submission of Matters to a Vote of Security Holders            4

ITEM 6.     Exhibits and Reports on Form 8-K                               4


SIGNATURES                                                                 5

                               Page 2 of 6 Pages
<PAGE>   3





PART I FINANCIAL INFORMATION

ITEM 1.     FINANCIAL STATEMENTS (SEE NOTE BELOW)

ITEM 2.     MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
            RESULTS OF OPERATIONS (SEE NOTE BELOW)

           Enron Capital Trust I (the "Trust") is a statutory business trust
created under the Delaware Business Trust Act, as amended (the "Trust Act"),
pursuant to an amended and restated declaration of trust (the "Declaration")
and the filing of a certificate of trust with the Secretary of State of the
State of Delaware. The Trust's sole assets are 8,247,440 8.30% Partnership
Preferred Securities ($25 liquidation amount per security) representing an 85%
limited partnership interest in Enron Preferred Funding, L.P., a Delaware
limited partnership (the "Partnership"). Ownership of the assets of the Trust
is evidenced by an aggregate of 8,000,000 8.30% Trust Preferred Securities (the
"Trust Preferred Securities"), which are listed and traded on the New York
Stock Exchange under the symbol "ENE PrT", and 247,440 Trust Common Securities
(the "Trust Common Securities," and, together with the Trust Preferred
Securities, the "Trust Securities"), all of which are owned by Enron Corp., an
Oregon corporation ("Enron"). The Trust makes distributions on the Trust
Securities to the extent it receives distributions from the Partnership on the
Partnership Preferred Securities. Payments on the Partnership Preferred
Securities represent the sole source of revenue for the Trust. Distributions on
the Trust Securities are guaranteed by Enron, but only to the extent that the
Trust has available funds to pay such distributions. The Trust was created for
the sole purpose of issuing the Trust Securities, investing the proceeds of
such issuance in the Partnership Preferred Securities and engaging in only
those other activities necessary or incidental thereto. The Trust Securities
are subject to redemption at any time on or after March 31, 2002 and earlier in
the event of certain tax law changes or other events.

           The general partner of the Partnership is Enron, which owns a 15%
general partnership interest in the Partnership. Since completion of the
offering of the Trust Preferred Securities on November 21, 1996, the assets of
the Partnership have been invested primarily in a $181,926,000 principal amount
7.75% Subordinated Debenture due 2016 of Enron (the "Enron Debenture") and
$29,108,000 principal amount 7.75% Debentures due 2016 of each of Enron Capital
& Trade Resources Corp. and Enron Pipeline Company (the "Subsidiary Debentures"
and, together with the Enron Debenture, the "Debentures"), each of which is a
wholly owned subsidiary of Enron. The obligations under the Subsidiary
Debentures are guaranteed by Enron. The respective issuers of the Debentures
have certain rights to elect to defer any payments of principal and interest on
the Debentures for up to five years at a time. In addition to the Debentures,
the Partnership owns an aggregate of approximately $2,540,835 in short-term,
investment grade debt securities (the "Eligible Debt Securities"). Under
certain circumstances, upon repayment of one or more of the Debentures, the
assets of the Partnership may be reinvested in one or more debt securities of
Enron or its subsidiaries. Payments of interest and principal on the Enron
Debenture and the Subsidiary Debentures (or the guarantees thereof) and the
Eligible Debt Securities are the sole source of revenue for the Partnership.
The Partnership pays distributions to the Trust as holder of the Partnership
Preferred Securities when, as and if Enron, as the general partner, determines
to do so, although Enron has no obligation to do so.

       NOTE: Because the Trust and the Partnership are special purpose
financing entities with no separate business operations, the only assets of the
Trust are the Partnership Preferred Securities, and substantially all of the
assets of the Partnership consist of a debt security of Enron and debt
securities of subsidiaries of Enron that are guaranteed by Enron, the Trust
does not believe that financial statements for the Trust or the Partnership are
meaningful. Accordingly, financial statements and related financial information
have not been included in this Form 10-Q. For further information concerning
Enron and its subsidiaries, including financial statements and other financial
information, see the Enron Annual Report on Form 10-K for the year ended
December 31, 1998, and Enron Quarterly Report on Form 10-Q for the quarterly
period ended June 30, 1999, as filed with the Securities and Exchange
Commission, copies of which may be obtained from the Corporate Secretary of
Enron at the address listed on the cover of this Form 10-Q.


                               Page 3 of 6 Pages
<PAGE>   4





PART II     OTHER INFORMATION

ITEM 1.     LEGAL PROCEEDINGS

            None.

ITEM 2.     CHANGES IN SECURITIES

            None.

ITEM 3.     DEFAULTS UPON SENIOR SECURITIES

            None.

ITEM 4.     SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

            None.

ITEM 6.     EXHIBITS AND REPORTS ON FORM 8-K

       (A)       EXHIBITS.

            4.1      Certificate of Trust (incorporated by reference to Exhibit
                     4(a) of the Registration  Statement on Form S-3 of the
                     Trust (No. 333-14967)).
            4.2      Amended and Restated Declaration of Trust dated as of
                     November 18, 1996 (incorporated by reference to Exhibit
                     4.2 to Enron Capital Trust I Form 10-K for the year ended
                     December 31, 1996 ("Form 10-K").
            4.3      Amended and Restated Agreement of Limited Partnership of
                     Enron Preferred  Funding L.P. dated as of November 21,
                     1996 (incorporated by reference to Exhibit 4.3 to
                     Form 10-K).
            4.4      Trust Preferred Guarantee Agreement dated as of November
                     21, 1996 (incorporated by reference to Exhibit 4.4 to
                     Form 10-K).
            4.5      Partnership Preferred Guarantee Agreement dated as of
                     November 21, 1996 (incorporated by reference to Exhibit
                     4.5 to Form 10-K).
            4.6      Indenture dated as of November 21, 1996 relating to the
                     Enron's 7.75% Subordinated Debentures due 2016
                     (incorporated by reference to Exhibit 4.6 to Form 10-K).
            4.7      Indenture dated as of November 21, 1996 relating to Enron
                     Pipeline Company's 7.75% Debentures due 2016
                     (incorporated by reference to Exhibit 4.7 to Form 10-K).
            4.8      Indenture dated as of November 21, 1996 relating to the
                     Enron Capital & Trade Resources Corp. 7.75% Debentures due
                     2016 (incorporated by reference to Exhibit 4.8 to Form
                     10-K).
            4.9      Guarantee Agreement of Enron dated as of November 21, 1996
                     relating to Enron Pipeline Company's 7.75% Debentures
                     due 2016 (incorporated by reference to Exhibit 4.9 to
                     Form 10-K).
            4.10     Guarantee Agreement of Enron dated as of November 21, 1996
                     relating to Enron Capital & Trade Resources Corp. 7.75%
                     Debentures due 2016 (incorporated by reference to Exhibit
                     4.10 to Form 10-K).
            4.11     Form of certificate representing Trust Preferred
                     Securities (included in Exhibit 4.2).
            27.1     Financial Data Schedule.

       (B)       REPORTS ON FORM 8-K.

                 None.


                               Page 4 of 6 Pages
<PAGE>   5





                                   SIGNATURES

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

                                                ENRON CAPITAL TRUST I
                                                      (Registrant)



Date: August 13, 1999                             /s/  PHILLIP M. SISNEROS
                                                -----------------------------
                                                Name:  Phillip M. Sisneros
                                                Title:    Regular Trustee



                               Page 5 of 6 Pages


<PAGE>   6



                               INDEX TO EXHIBITS

          EXHIBIT
            NO.                         DESCRIPTION

            4.1      Certificate of Trust (incorporated by reference to Exhibit
                     4(a) of the Registration  Statement on Form S-3 of the
                     Trust (No. 333-14967)).
            4.2      Amended and Restated Declaration of Trust dated as of
                     November 18, 1996 (incorporated by reference to Exhibit
                     4.2 to Enron Capital Trust I Form 10-K for the year ended
                     December 31, 1996 ("Form 10-K").
            4.3      Amended and Restated Agreement of Limited Partnership of
                     Enron Preferred  Funding L.P. dated as of November 21,
                     1996 (incorporated by reference to Exhibit 4.3 to
                     Form 10-K).
            4.4      Trust Preferred Guarantee Agreement dated as of November
                     21, 1996 (incorporated by reference to Exhibit 4.4 to
                     Form 10-K).
            4.5      Partnership Preferred Guarantee Agreement dated as of
                     November 21, 1996 (incorporated by reference to Exhibit
                     4.5 to Form 10-K).
            4.6      Indenture dated as of November 21, 1996 relating to the
                     Enron's 7.75% Subordinated Debentures due 2016
                     (incorporated by reference to Exhibit 4.6 to Form 10-K).
            4.7      Indenture dated as of November 21, 1996 relating to Enron
                     Pipeline Company's 7.75% Debentures due 2016
                     (incorporated by reference to Exhibit 4.7 to Form 10-K).
            4.8      Indenture dated as of November 21, 1996 relating to the
                     Enron Capital & Trade Resources Corp. 7.75% Debentures due
                     2016 (incorporated by reference to Exhibit 4.8 to Form
                     10-K).
            4.9      Guarantee Agreement of Enron dated as of November 21, 1996
                     relating to Enron Pipeline Company's 7.75% Debentures
                     due 2016 (incorporated by reference to Exhibit 4.9 to
                     Form 10-K).
            4.10     Guarantee Agreement of Enron dated as of November 21, 1996
                     relating to Enron Capital & Trade Resources Corp. 7.75%
                     Debentures due 2016 (incorporated by reference to Exhibit
                     4.10 to Form 10-K).
            4.11     Form of certificate representing Trust Preferred
                     Securities (included in Exhibit 4.2).
            27.1     Financial Data Schedule.

                               Page 6 of 6 Pages