The semideciduous seasonal forest, physiognomy that covered almost the entire interior of the São Paulo state, is currently represented by only 5% of its original area. This paper presents a survey of mimosoid clade in one of the last areas of continuous vegetation of the state, the Serra do Japi. Twenty four species belonging to eight genera were sampled, of which Mimosa (7 spp.), Inga (6 spp.), Senegalia (5 spp.) and Anadenanthera (2 spp.) were the most diverse genera. The arboreal taxa prevail on this area. Inventoried species are well distributed in the different vegetation types of Brazil. Twelve species are new records for the Serra do Japi and one species to the state. Six species are endemic to Brazil (Abarema langsdorffii, Inga subnuda, I. sessilis, Leucochloron incuriale, Mimosa furfuracea, Senegalia grandistipula) and two only occur in the Mata Atlântica (Inga subnuda e Senegalia grandistipula).The main diagnostic characters to distinguish the genera, were the types of leaf and fruit, presence of extrafloral nectaries and number and fusion of stamens, and for the species, presence of glands in specific locations, presence of thorns, trichomes and stipules, and number of leaflets.