This study was carried out at the ‘Mario Viana’ Municipal Biological Reserve in Nova Xavantina, MT, aiming to make an inventory and evaluate the abundance and diversity of terrestrial mammals of medium and large size. Thus, two monthly visits were made to a 2.820 m long transect throughout 2001 to assess tracking and other evidences of mammals. Twenty-nine species were recorded in the study area, with 22 in the transect and two individual tracking sequences being quantified for calculation of the Shannon-Wiener (H’) abundance and diversity indices. According to the abundance indices, the species were classified as rare, common and abundant. Among other species, onça-parda (Puma concolor (Linnaeus, 1771)) and tatucanastra (Priodontes maximus (Keer, 1792) were classified as rare; jaguatirica (Leopardus pardalis (Linnaeus, 1758)) and tamanduá-bandeira (Myrmecophaga tridactyla Linnaeus, 1758) as common; and cutia (Dasyprocta azarae (Lichtenstein, 1823)) and tapetí (Sylvilagus brasiliensis (Linnaeus, 1758)) as abundant species. The H’ index found was 2.40, which was considered significant. This work shows that despite being small (470 ha), the area studied plays an important role in the preservation of the mammalian fauna in the region of Nova Xavantina, MT.