The Atlantic Forest in the state of Rio de Janeiro is extremely fragmented and reduced in its original extension. Although there are a great number of studies related to the biome, few lists are available for this region. The present study seeks to get information on the mammals of a remnant forest in Serra da Concórdia, an area from which no information is currently available. The rapid mammal's survey was accomplished by use of pitfalls, live traps, transects, mist nets, and camera traps. We recorded 37 terrestrial species that represent 22.3 % of Rio de Janeiro state mammal species. Among the recorded species, six are endemic of the Atlantic Forest, one is endemic of the state, and eight are in the state list of threatened or presumably threatened species. The area presents great mammal richness and an increasing effort will probably reveal the presence of additional species.