The present report is based upon two collections of seaweeds by the members of the Institute of Oceanology in 1957 and 1958 from the Xisha Islands--a group of South China Sea coral islands located about 170 miles southeast from Yulingkang of the Hainan Island, between 15°46'and 17°8'N, and 110°11' and 112°54' E. The algal flora of these coral islands is very imperfectly known. In their report on the Chinese species of Dictyosphaeria by Tseng and C. F. Chang (1962), four species including one new species D. spinifera were from Xisha Islands. In his study of the distribution of Chinese Siphonocladales, Fan (1963) listed 14 species including these four species. In the present paper twenty species belonging to ten genera and four families are reported, of which six species including two new species are recorded for the first time from Xisha Islands.