The present work documents the diversity of mammals in the headwaters of the Apurímac river, one of the most important information gaps in Peru, based on an evaluation of fi ve sampling areas in the departments of Apurímac (Cconoc, Velavelayoc), Ayacucho (Yanamonte, Ccentabamba) and Cuzco (Catarata). Capture’s effort was 1280 trap-nights and 41 mistnet-nights. Sixty species were recorded in the study area and included 15 threatened species and four species endemic to Perú. As expected, bats and rodents were the most diverse orders (66,7 %). The species diversity in the sites sampled declines signifi cantly with elevation from the lowest elevation sites (Ccentabamba and Catarata) to the highest (Velavelayoc). The marsupial Monodelphis peruvi...