San Martín Lachilá is a town and municipality in Oaxaca in south-western Mexico.

The municipality covers an area of 49.76 km2.

It is part of the Ejutla District in the south of the Valles Centrales Region.

As of 2005, the municipality had a total population of 979.

This article about a location in the Mexican state of Oaxaca is a stub.