The present paper deals with the Mytilidae colleeted from the Xisha Islands by the Institute of Oceanology, Academia Sinica, during 1956-1976.A total of 116 specimens of Mytilidae is studied and 11 species belonging to 6 genera are identified. Of these, three are new and three species, viz. Gregariella coralliophaga (Gmelin ) Lithophaga (Deliolabis )lithura Pilsbry and Lithophaga (Stumpiella) calyculata (Carpenter),are recorded for the first time from Chinese waters..Type specimens are deposited in the Institute of Oceanology, Academia Sinica, Qingdao, Shandong Province, China.