(Uploaded by Plazi for the Bat Literature Project) Phyllostomids are locally abundant, ecologically diverse, and form rich assemblages. They also provide essential ecosystem services, which may change along the year in response to changes in bat abundances. Here we report on a phyllostomid assemblage studied at Reserva Biológica União (RBU), an Atlantic Forest area with outstanding diversity in southeastern Brazil. We assessed seasonal variation in diversity profiles for alpha and beta components, as well as in the abundance of the most common species. Spatial variation in phyllostomid diversity profiles and components was also assessed, using published information from three nearby sites. Based on a sample of 786 mist net captures and records from monitored roosts, the phyllostomid assemblage at RBU was found to include at least 19 species, two of which recognized as endangered at the national level (Lonchorhina aurita and Lonchophylla peracchii). The diversity profile for RBU was heavily influenced by common species and was one of the richest but less diverse in the region due to its uneven distribution. The diversity profiles suggested no seasonal differences in alpha diversity. Beta diversity profiles for spatial and seasonal analyses showed that samples behaved as subsets of a single assemblage, suggesting a relative homogeneity of resources in these dimensions. At the population level, however, some expected seasonal variation in abundance was confirmed (e.g., in Artibeus spp. and in Carollia perspicillata). The high relative frequency of Sturnira tildae at RBU differentiated this site, thus reinforcing its conservation importance.