ABSTRACT The Cerrado is the second largest Brazilian biome and only 2.8% is represented by protected areas. Considering the relevance of the Cerrado and Conservation Units in preserving the mammalian diversity, we provided the first assessment of the diversity of medium- and large-sized mammal species in the Chapada dos Veadeiros National Park (CVNP) and surroundings. We tested the effectiveness of the CVNP by assessing the difference in species composition within the park and its surroundings. We sampled CVNP in the rainy (October-December 2013) and dry seasons (March-June 2014) in order to characterize the seasonality within the community. We selected 36 sampling sites to evaluate the composition of the medium and large mammals in the CVNP and its surroundings, 18 in the CVNP and 18 in the park surroundings. We ordered mammalian composition and frequency of individuals data by using a Non-metric Multidimensional Scaling analysis (NMDS). We assessed the effect of season (dry and rainy seasons) and locality (within the CVNP and surroundings) on mammalian species richness with a two-way analysis of variance (Two-way ANOVA). We recorded 23 species, 13 within the CVNP and 17 species in its surroundings. Composition and frequency of records differed between dry and rainy seasons, with higher richness in the rainy season. Species’ composition and the frequency of records were also different between within the CVNP and its surroundings, with higher richness in the surroundings. These results provide information for the increase of the knowledge of mammalian ecology but also is useful as a tool for future strategies to the conservation of these species. More attention should be given to the monitoring of these species in the long term because this area still harbor some viable populations.