A comparative study was made on the composition of the vagile fauna Inhabiting the alga Sargassum cymosum collected at 2 sites, d~f f e r~n g in wave action, on the northern coast of Sao Paulo State, Braz~l (23"30'S and 45"06'W). A total of 122.886 specimens were collected at 2 stdt~ons, belonging to 23 taxonomic groups. Gammaridea comprised the dominant group at both sites. 15 species were recorded, among these 14 common specles. Water rn0vemen.t -even at the exposed shore -and sediment quantlty of the sheltered site do not seem to affect gamrnaridean specles variety. Species dominance thl-oughout the yedr varied In exposed and sheltered localities. Hyale medla was dominant at the exposed shore, and Amphilochus neapolitanus was the most abundant species at the sheltered shore.