The state of Rondônia harbors 185 of the 399 species of mammals recorded from the Amazon biome, which corresponds to 46.4% of the total number of species. The state is also an important center of diversity and endemism, especially due to the presence of major biogeographical barriers such as the rio Madeira. We employed trap cameras and track surveys to assess the mammal community in the Base de Selva da Polícia Militar in Rondônia state, Brazil. During one year of survey, we recorded 40 species of medium-sized and large mammals, and, in our study, we recorded the highest mammal richness for a locality in Rondônia, which highlights the importance of private protected areas for mammal conservation in the state. Camera-trap records also showed the occurrence of threatened species. Finally, we provide recommendations for additional studies in this region that is threatened by deforestation and expansion of agriculture.