<PAGE>   1

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                                 UNITED STATES

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   FORM 10-Q

(MARK ONE)

[X]   QUARTERLY REPORT UNDER SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT
      OF 1934

FOR THE QUARTERLY PERIOD ENDED                SEPTEMBER 30, 2000               .

                                       OR

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

FOR THE TRANSITION PERIOD FROM  _____________________ TO
 _____________________  .

COMMISSION FILE NO. 2-80930

                        DEL TACO RESTAURANT PROPERTIES I
                        A CALIFORNIA LIMITED PARTNERSHIP
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

<TABLE>
<S>                                                     <C>
                      CALIFORNIA                                  95-3852699
            (STATE OR OTHER JURISDICTION OF                    (I.R.S. EMPLOYER
            INCORPORATION OR ORGANIZATION)                  IDENTIFICATION NUMBER)

 23041 AVENIDA DE LA CARLOTA, LAGUNA HILLS, CALIFORNIA              92653
       (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES)                   (ZIP CODE)
</TABLE>

                                 (949) 462-9300
              (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.  YES [X]  NO [ ]

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                                      INDEX

                        DEL TACO RESTAURANT PROPERTIES I

<TABLE>
<CAPTION>

PART I.  FINANCIAL INFORMATION                                           PAGE NUMBER
------------------------------                                           -----------
<S>                                                                      <C>

Item 1.  Financial Statements and Supplementary Data


Balance Sheets at September 30, 2000 (Unaudited) and
     December 31, 1999                                                      3

Statements of Income for the three and nine months ended
     September 30, 2000 and 1999 (Unaudited)                                4

Statements of Cash Flows for the nine months ended
     September 30, 2000 and 1999 (Unaudited)                                5

Notes to Financial Statements                                               6


Item 2.  Management's Discussion and Analysis of
         Financial Condition and Results of Operations                      8


PART II. OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K                                  10


SIGNATURES                                                                 11
</TABLE>


                                      -2-
<PAGE>   3




                        DEL TACO RESTAURANT PROPERTIES I

                                 BALANCE SHEETS

<TABLE>
<CAPTION>

                                             SEPTEMBER 30,    December 31,
                                                 2000             1999
                                             -------------    ------------
                                              (UNAUDITED)
                                     ASSETS

<S>                                          <C>              <C>
CURRENT ASSETS:
     Cash                                     $  201,482      $  170,290
     Receivable from General Partner              51,484          46,970
     Deposits                                        600             600
                                              ----------      ----------
        Total current assets                     253,566         217,860
                                              ----------      ----------

PROPERTY AND EQUIPMENT, AT COST:
     Land and improvements                     1,852,482       1,852,482
     Buildings and improvements                1,013,134       1,013,134
     Machinery and equipment                   1,136,026       1,136,026
                                              ----------      ----------
                                               4,001,642       4,001,642
     Less--accumulated depreciation            1,792,688       1,759,859
                                              ----------      ----------
                                               2,208,954       2,241,783
                                              ----------      ----------
                                              $2,462,520      $2,459,643
                                              ==========      ==========

                        LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
     Payable to Limited Partners              $   40,829      $   31,001
     Accounts payable                             10,000           7,828
                                              ----------      ----------
        Total current liabilities                 50,829          38,829
                                              ----------      ----------

PARTNERS' EQUITY:
     Limited Partners                          2,147,477       2,156,509
     General Partner-Del Taco, Inc.              264,214         264,305
                                              ----------      ----------
                                               2,411,691       2,420,814
                                              ----------      ----------
                                              $2,462,520      $2,459,643
                                              ==========      ==========
</TABLE>




                          The accompanying notes are an
                   integral part of these financial statements

                                      -3-

<PAGE>   4




                        DEL TACO RESTAURANT PROPERTIES I

                              STATEMENTS OF INCOME

                                   (UNAUDITED)


<TABLE>
<CAPTION>
                                       Three Months Ended          Nine Months Ended
                                          September 30,               September 30,
                                       2000          1999          2000          1999
                                     --------      --------      --------      --------
<S>                                  <C>           <C>           <C>           <C>

REVENUES:
     Rent                            $155,809      $141,151      $434,944      $397,688
     Interest                           1,784         1,222         4,151         3,304
     Other                                350           353           725           953
                                     --------      --------      --------      --------
                                      157,943       142,726       439,820       401,945
                                     --------      --------      --------      --------

EXPENSES:
     General and administrative         7,311         7,199        38,186        38,225
     Depreciation                      10,943        10,943        32,829        32,829
                                     --------      --------      --------      --------
                                       18,254        18,142        71,015        71,054
                                     --------      --------      --------      --------

        Net income                   $139,689      $124,584      $368,805      $330,891
                                     ========      ========      ========      ========

     Net income per limited
        partnership unit             $  15.80      $  14.09      $  41.72      $  37.43
                                     ========      ========      ========      ========
</TABLE>



                                      -4-



                          The accompanying notes are an
                  integral part of these financial statements.


<PAGE>   5




                        DEL TACO RESTAURANT PROPERTIES I

                            STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)


<TABLE>
<CAPTION>
                                                                     NINE MONTHS ENDED
                                                                       SEPTEMBER 30,
                                                                   2000            1999
                                                                 ---------       ---------
<S>                                                              <C>             <C>

CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                                       $ 368,805       $ 330,891
Adjustments to reconcile net income to net
  cash provided by operating activities:
     Depreciation                                                   32,829          32,829
     (Increase) decrease in receivable from General Partner         (4,514)          2,179
     Decrease in deposits                                                -             113
     Increase in accounts payable and payable
        to limited partners                                         12,000             252
                                                                 ---------       ---------

           Net cash provided by operating activities               409,120         366,264


CASH FLOWS FROM FINANCING ACTIVITIES:

Cash distributions to partners                                    (377,928)       (363,958)
                                                                 ---------       ---------

Net increase in cash                                                31,192           2,306

Beginning cash balance                                             170,290         162,979
                                                                 ---------       ---------
Ending cash balance                                              $ 201,482       $ 165,285
                                                                 =========       =========
</TABLE>



                                      -5-

                          The accompanying notes are an
                  integral part of these financial statements.


<PAGE>   6




                        DEL TACO RESTAURANT PROPERTIES I

                          NOTES TO FINANCIAL STATEMENTS

                               SEPTEMBER 30, 2000


NOTE 1 - BASIS OF PRESENTATION

The accompanying financial statements, some of which are unaudited, have been
prepared in accordance with generally accepted accounting principles for interim
financial information and with the instructions to Form 10-Q and Article 10 of
Regulation S-X. Accordingly, they do not include all of the information and
footnotes required by generally accepted accounting principles for complete
financial statements and should therefore be read in conjunction with the
financial statements and notes thereto contained in the Registrant's annual
report on Form 10-K for the year ended December 31, 1999. In the opinion of
management, all adjustments (consisting of normal recurring accruals) necessary
to present fairly the partnership's financial position at September 30, 2000,
the results of operations and cash flows for the nine month periods ended
September 30, 2000 and 1999 have been included. Operating results for the three
and nine months ended September 30, 2000 are not necessarily indicative of the
results that may be expected for the year ending December 31, 2000.

NOTE 2 - NET INCOME PER LIMITED PARTNERSHIP UNIT

Net income per limited partnership unit is based upon the weighted average
number of units outstanding during the periods presented, which amounted to
8,751 in 2000 and 1999.

Pursuant to the partnership agreement, annual partnership net income is
allocated one percent to the General Partner and 99 percent to the limited
partners. A partnership net loss in any year will be allocated 24 percent to the
General Partner and 76 percent to the limited partners until the losses so
allocated equal income previously allocated. Any additional losses will be
allocated one percent to the General Partner and 99 percent to the limited
partners. Partnership gains from any sale or refinancing will be allocated one
percent to the General Partner and 99 percent to the limited partners until
allocated gains and profits equal losses. Additional gains will be allocated 24
percent to the General Partner and 76 percent to the limited partners.



                                      -6-
<PAGE>   7




                        DEL TACO RESTAURANT PROPERTIES I

                    NOTES TO FINANCIAL STATEMENTS - CONTINUED

                               SEPTEMBER 30, 2000


NOTE 3 - LEASING ACTIVITIES

The partnership leases certain properties for operation of restaurants to Del
Taco, Inc. on a triple net basis. The leases are for terms of 35 years
commencing with the completion of the restaurant facility located on each
property and require monthly rentals equal to 12 percent of the gross sales of
the restaurants. There is no minimum rental under any of the leases.

For the three months ended September 30, 2000, the five restaurants operated by
Del Taco, for which the partnership is the lessor, had combined, unaudited sales
of $1,079,113 and net income of $68,143 as compared to $977,544 and $61,546
respectively, for the corresponding period in 1999. Net income by restaurant
includes charges for general and administrative expenses incurred in connection
with supervision of restaurant operations and interest expense. For the three
months ended September 30, 2000, the one restaurant operated by a Del Taco
franchisee, for which the partnership is the lessor, had unaudited sales of
$219,297 as compared with $198,717 during the same period in 1999.

For the nine months ended September 30, 2000, the five restaurants operated by
Del Taco, for which the partnership is the lessor, had combined, unaudited sales
of $3,013,010 and net income of $173,243 as compared to $2,756,556 and $140,234
respectively, for the corresponding period in 1999. For the nine months ended
September 30, 2000, the one restaurant operated by a Del Taco franchisee, for
which the partnership is the lessor, had unaudited sales of $611,520 as compared
with $557,517 during the same period in 1999.

For the three months and nine months ended September 30, 2000, the Elkhorn
Boulevard restaurant in Sacramento, California reported net income of $4,058 and
$871 as compared to net losses of $1,986 and $6,927 for the corresponding
periods in 1999.

NOTE 4 - TRANSACTIONS WITH DEL TACO

The receivable from General Partner consists primarily of rent accrued for the
month of September. The September rent receivable was collected on October 13,
2000.

Del Taco, Inc. serves in the capacity of general partner in other partnerships
which are engaged in the business of operating restaurants, and three other
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.

In addition, see Note 5 with respect to certain distributions to the General
Partner.

NOTE 5 - DISTRIBUTIONS

On October 13, 2000, a distribution to the limited partners of $154,097, or
approximately $17.61 per limited partnership unit, was approved. Such
distribution was paid on October 18, 2000. The General Partner also received a
distribution of $1,557 with respect to its 1% partnership interest.

                                      -7-
<PAGE>   8




ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

Liquidity and Capital Resources

The partnership offered limited partnership units for sale between March 1983
and March 1984. 15% of the $4.375 million raised through sale of limited
partnership units was used to pay commissions to brokers and to reimburse the
General Partner for offering costs incurred. Approximately $4 million of the
remaining funds were used to acquire sites and build six restaurants.

The six restaurants leased to Del Taco make up almost all of the income
producing assets of the partnership. Therefore, the business of the partnership
is almost entirely dependent on the success of the Del Taco trade name
restaurants that lease the properties. The success of the restaurants is
dependent on a large variety of factors, including, but not limited to, consumer
demand and preference for fast food, in general, and for Mexican-American food
in particular.

Results of Operations

The partnership owns six properties that are under long-term lease to Del Taco
for restaurant operations (Del Taco, in turn, has subleased two of the
restaurants to Del Taco franchisees, one of which is affiliated with Del Taco).

The following table sets forth rental revenue earned by restaurant for the year:

<TABLE>
<CAPTION>

                                                   THREE MONTHS ENDED              NINE MONTHS ENDED
                                                      SEPTEMBER 30,                   SEPTEMBER 30,
                                                  2000            1999            2000            1999
                                                --------        --------        --------        --------
<S>                                             <C>             <C>             <C>             <C>
Riverside Avenue, Rialto, CA                    $ 23,008        $ 22,671        $ 66,464        $ 64,123

Elden Avenue, Moreno Valley, CA                   25,134          20,736          71,304          59,543

Foothill Boulevard, La Verne, CA                  33,202          30,650          91,317          86,111

Baseline & Archibald, Rancho Cucamonga, CA        26,316          23,846          73,382          66,902

Elkhorn Boulevard, Sacramento, CA                 18,274          16,233          48,496          45,140

Haven Avenue, Rancho Cucamonga, CA                29,875          27,015          83,981          75,869
                                                --------        --------        --------        --------
        Total                                   $155,809        $141,151        $434,944        $397,688
                                                ========        ========        ========        ========
</TABLE>


The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $155,809 during the
three month period ended September 30, 2000, which represents an increase of
$14,658 from 1999. The partnership earned rental revenue of $434,944 during the
nine month period ended September 30, 2000, which represents an increase of
$37,256 from 1999. The changes in rental revenue between 1999 and 2000 are
directly attributable to increases in sales levels at the restaurants under
lease.



                                      -8-
<PAGE>   9




ITEM 2. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS - CONTINUED

The following table breaks down general and administrative expenses by type of
expense:

<TABLE>
<CAPTION>

                                                     Percentage of Total
                                              General & Administrative Expense
                                              --------------------------------

                                                     Nine Months Ended
                                                       September 30,
                                                     2000         1999
                                                   -------       ------
<S>                                                  <C>           <C>
Accounting fees                                      59.90%        67.68%
Distribution of
  information to
  Limited Partners                                   40.10         32.32
                                                    ------        ------
                                                    100.00%       100.00%
                                                    ======        ======
</TABLE>

For the three month period ended September 30, 2000, net income increased
$15,105 from 1999 to 2000 due to the increase in revenues of $15,217 which was
partially offset by the $112 increase in general and administrative expenses.
For the nine month period ended September 30, 2000, net income increased by
$37,914 from 1999 to 2000 due to the increase in revenues of $37,875 and the $39
decrease in general and administrative expenses.


                                      -9-

<PAGE>   10




PART II.  OTHER INFORMATION

Item 6.  Exhibits and Reports on Form 8-K

(b) No reports on Form 8-K were filed during the nine months ended September 30,
2000.




                                      -10-
<PAGE>   11






                                   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.


                                            DEL TACO RESTAURANT PROPERTIES I
                                            (a California limited partnership)
                                            Registrant

                                            Del Taco, Inc.
                                            General Partner



Date:  October 31, 2000                     /s/ Robert J. Terrano
                                            ----------------------------
                                            Robert J. Terrano
                                            Executive Vice President,
                                            Chief Financial Officer


Date:  October 31, 2000                     /s/ C. Douglas Mitchell
                                            ----------------------------
                                            C. Douglas Mitchell
                                            Vice President and Corporate
                                            Controller


                                      -11-

<PAGE>   12

                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
Exhibit
Number                   Description
-------                  -----------
<S>                      <C>
27.1                     Financial Data Schedule
</TABLE>


                                      -12-