Plaza San Martín, Central plaza in Historic Centre of Lima, Peru.

Plaza San Martín is a central square in the Historic Centre of Lima, Peru, with a bronze equestrian monument in the middle and neocolonial buildings surrounding it. The square is paved with granite slabs and framed by marble benches that offer seating for visitors.

The site held the San Juan de Dios hospital, demolished in 1850, then a railway station torn down between 1911 and 1918. The plaza was authorized on 6 July 1917 and inaugurated on 27 July 1921 by President Augusto B. Leguía for the independence centenary. In 1825 Bernardo de Monteagudo was assassinated on the adjacent Plazoleta de la Micheo.

The square is named after José de San Martín, who led Peru's independence, and its bronze equestrian monument by Mariano Benlliure shows him crossing the Andes. The plaza has long served as Lima's protest ground: in 1987 Mario Vargas Llosa led a rally here against the nationalization of banks, and in 2020 demonstrations here pushed President Manuel Merino to resign.

The square sits at the ninth block of Colmena Avenue and connects to Plaza Mayor through the pedestrian street Jirón de la Unión. The area is busy during daytime and works well as a short stop during a walk through the center.

The bronze figure of Madre Patria at the monument's base wears a small llama on her head, which came from a Spanish translation error. The mistake was never corrected and remains a detail many visitors overlook.