The seagrass Porieresia coarctata grown in two habitats, viz., Prentice and Chuksar Islands of Sunderbans mangrove ecosystem, were studied for their sterol and triterpenoid constituents. Major sterols were sitosterol and stigmasterol; other components were campesterol and cholesterol. Major pentacyclic triterpenoids were lupeol and oleanolic acid, other components were. (.-aniyrin, /3-amyrin and ursolic acid. Considerable quantitative differences were observed in the sterol and triterpenoid compositions. Among the triterpenoids betulin was found to occur only in the sample of Chuksar Island