The Sierra Madre del Sur is a mountain range in southern Mexico, extending 1000 km from southern Michoacán east through Guerrero, to the Istmo de Tehuantepec in eastern Oaxaca. It joins with the Eje Volcánico Transversal of central Mexico in northern Oaxaca, but is separated from this range further west by the valley of the Río Balsas and its tributary the Río Tepalcatepec.
The highest point is 3703 m, located at in central Guerrero.
Although separated from the main part of the Sierra Madre del Sur by the deep canyon of the lower Río Balsas, the mountains of southern Michoacán around Coalcomán are usually considered part of the Sierra Madre del Sur.
The Sierra Madre del Sur pine-oak forests occupy the higher reaches of the range. These forests are part of a chain of pine-oak forests that stretch from the southwestern United States to Costa Rica along the American Cordillera.
Lower elevations of the range are covered by tropical dry forests. The Jalisco dry forests occupy the western end of the range's Pacific slope. The Southern Pacific dry forests occupy most of the Pacific slope of the range, from Michoacan in the west through Guerrero and Oaxaca. The basin of the Balsas River, north of the Sierra, is home to the Balsas dry forests.