Medium and large mammals in Sierra de Villa Alta, Oaxaca, Mexico. The Sierra Madre de Oaxaca (SMO) is one of the most biologically diverse subprovinces of Oaxaca. However, there are still regions that have not been explored, leading to gaps in the knowledge of mammals; particularly in areas far away from roads. In order to fill these gaps, we generated an inventory of medium and large mammals in the Sierra de Villa Alta. We used indirect methods, mammal tracks search and local people interviews, as well as direct observations from July 2005 to August 2006. We reported a total of 18 mammal species, the greatest species richness corresponds to the Orden Carnivora (n = 8), followed by Rodentia (n = 3) and Artiodactyla (n = 3). The trophic guilds are represented mainly by herbivores (n = 5) and omnivores (n = 5). Regarding the biogeographic affinity, the region consists mainly of species with a distribution shared by Nearctic and Neotropical regions (n = 9). We registered three endangered species by mexican law: Potos flavus (threatened), Tamandúa mexicana and Panthera onca (endangered), the last one listed as near threatened by the IUCN. The local people recognize 25 species, of which we found no evidence for seven.