In a tropical dry forest of northwestern Madagascar, brown lemur (Eulemur fulvus) is the sole large-bodied frugivore that can swallow large seeds (seed diam. > 10 mm). To investigate the role as a large seed disperser, I recorded the feeding activities of a troop; I also conducted fecal analyses, germination trials on defecated seeds, and a vegetation survey over one year. Brown lemurs mostly consumed fruit (68%). Among dung samples, 1126 contained intact seeds of 70 plant species, with a median of 6 seeds and 2 species per sample. These data indicate that the brown lemur population dispersed approximately 9854 seeds/km²/day. Twenty-three species of large-seeded plants were probably dependent on brown lemurs for seed dispersal and some of them were common trees in the forest. In the species level, the fruit of Vitex beraviensis was the most exploited resource. Although the number of annually defecated seeds was large in several small-seeded plants, many of the small seeds were often clumped in dung piles. In contrast, large seeds of V. beraviensis occurred in the largest number of dung samples and the germination rate was high. Therefore, V. beraviensis may readily establish seedlings in sites of brown lemur fecal deposition. Maintenance of these key interactions will contribute to the conservation of species diversity and intact regeneration of a Madagascan forest.