National Astronomical Observatory of San Pedro Mártir, Astronomical research center in Baja California, Mexico.

The National Astronomical Observatory of San Pedro Mártir stands at 2,800 m in the Sierra San Pedro Mártir, in Ensenada, Baja California. Its white cylindrical building carries a hemispherical dome ringed by a blue band and a narrow railed platform; a tall blue door reached by steps opens at the base, a metal staircase with landings climbs the right side, and a small rectangular window sits on the left. The 2.1 m reflector, Mexico's largest optical telescope, was designed by José de la Herrán.

The observatory was founded in 1878 on the balcony of Chapultepec Castle in Mexico City, later moving to the Palacio del Ex-Arzobispado in Tacubaya. In 1967, air and light pollution drove it from Tonantzintla, Puebla, to the summit of the Sierra San Pedro Mártir. The 2.12 m telescope was built there between 1974 and 1979.

Researchers from Mexico and other countries work together at this facility to study the stars and planets. This international collaboration brings scientists together to share discoveries about space and the cosmos.

The site sits at high altitude, so visitors should allow time to adjust to the elevation and bring warm clothing. Tours are available but require advance booking and typically occur during nighttime hours when observations are most effective.

The 1.0 m SAINT-EX telescope, installed in 2019, searches for terrestrial planets around ultra-cool stars such as TRAPPIST-1. It is a collaboration between UNAM and the universities of Bern, Liège, Cambridge and Geneva, with Didier Queloz, Michaël Gillon and Brice Demory among the researchers involved.