We investigated the richness, composition, and species relative abundance of a terrestrial small mammal community in a Deciduous Forest area in the austral boundary of the Atlantic Forest. The microhabitat use of the most common species was also investigated. Six rodents - Akodon montensis (Thomas, 1913), Oligoryzomys nigripes (Olfers, 1818), Sooretamys angouya (Thomas, 1913), Thaptomys nigrita (Lichtenstein, 1829), Mus musculus (Linnaeus, 1758) and Juliomys sp. - and one marsupial - Didelphis albiventris (Lund, 1840) - were captured. Thaptomys nigrita is recorded in the state of Rio Grande do Sul for the first time. Species richness was poor when compared with communities in the central portions of the Atlantic Forest, but equivalent to that found in the Araucaria and Dense Ombrophilous forests of southern Brazil. The species most often captured in our study, A. montensis and O. nigripes, are also the most common in the majority of faunistic studies carried out in the Atlantic Forest. Akodon montensis and S. angouya used places with high abundance of bamboo, possibly to avoid predators. Oligorizomys nigripes used areas with a high density of scrubs, what could facilitate aboveground movements, and was negatively correlated to mature forest indicators, which reinforce the idea that this species has opportunistic habits.