San Martín Itunyoso is a Trique language town and municipality in Oaxaca in south-western Mexico.

The municipality covers an area of 82.93 km2.

It is part of the Tlaxiaco District in the south of the Mixteca Region.

As of 2005, the municipality had a total population of 2,554.

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