The LV Legislature of the Congress of the Union of Mexico (55th Congress) met from 1 September 1991 to 31 August 1994.

The deputies served three years and the senators six, continuing into the 56th Congress.

The PRI regained near-total control of the legislature, with nearly two-thirds of the deputies and all but three senators.

The Chamber of Deputies had 500 legislators, elected for three-year terms with no immediate reelection.

300 deputies were elected from single-member districts and the other 200 from party lists in each of the five proportional representation electoral regions.