Article 56 Political Constitution of the United Mexican States
Third Title · Chapter II. On the Legislative Power · Section I. On the Election and Installation of the Congress
Current text · last reform published in the Official Gazette of the Federation (DOF) on 2 June 2026
The Senate shall be integrated by one hundred twenty-eight senators, of which, in each State and in Mexico City, two shall be elected according to the principle of relative majority voting and one shall be assigned to the first minority. For these effects, the political parties must register a list with two formulas of candidates. The senatorship of first minority shall be assigned to the formula of candidacies that heads the list of the political party that, by itself, has occupied the second place in number of votes in the state (federal entity) in question.
The thirty-two remaining senatorships shall be elected according to the principle of proportional representation, through the system of lists voted in a single national plurinominal circumscription, formed in accordance with the principle of parity, and headed alternately between women and men each electoral period. The law shall establish the rules and formulas for these effects.
The Senate shall be renewed in its totality every six years.