| Unified Socialist Party of Mexico | |
| Native Name: | Partido Socialista Unificado de México |
| Foundation: | 18 December 1981 |
| Dissolved: | 1987 |
| Merger: | PCM PPM |
| Merged: | Mexican Socialist Party |
| Ideology: | Communism Anti-imperialism Multi-tendency |
| Position: | Far-left |
| State: | Mexico |
The Unified Socialist Party of Mexico (Spanish; Castilian: Partido Socialista Unificado de México, PSUM) was a socialist political party in Mexico. It later became the Mexican Socialist Party (Spanish; Castilian: Partido Mexicano Socialista) in 1988.
The PSUM was founded in November 1981 by the merger of four socialist parties:
Before merging to form the PSUM, these four parties had formed an electoral alliance called the Coalition of the Left (Spanish; Castilian: Coalición de Izquierda) in 1977.
Though the PSUM was a multi-tendency organization, it generally followed the ideology of Eurocommunism. In 1988, the PSUM changed its name to the Mexican Socialist Party (Spanish; Castilian: Partido Mexicano Socialista, PMS) after the merging with Mexican Workers' Party. In 1989, following the presidential campaign of Cuauhtémoc Cárdenas, the PMS joined Cárdenas and other dissidents from the Institutional Revolutionary Party to form the Party of the Democratic Revolution (PRD).