Macrobrachium is distributed globally in most biogeographical regions, and contains species with interesting mechanisms of evolution. We conducted an exhaustive survey on São Sebastião Island, the largest coastal island of the state of São Paulo. Here we provide a list of species (M. acanthurus, M. carcinus, M. heterochirus, M. olfersi, M. potiuna) together with the diagnosis, distribution, and remarks on each species, and a key for their identification. We compare our findings with available information on the genus. The high diversity of freshwater shrimps on the island is interesting in terms of biogeographical and evolutionary processes.