Our recent investigations have shown that the Xisha Islands(Guangdong Province, China )have a rich corallinaceous flora. In the present paper, six of the commoner species are reported. With the exception of Jania adhaerens Lamx, already reported from our Taiwan Province, the other five species, namely, Porolithon onkodes (Heydr.) Foslie, Hydrolthon reinboldii (Web. v. Bosse et Foslie) Foslie, Neogoniolithon frutescens (Foslie) Setch. et Mason, Amphiroa fragilissima (Linn.) Lamx. And Jania radiata Yendo, are recorded for the Chinese marine flora for the first time. An analysis of the corallinaceous components of the coral reefs of the Xisha Islands shows that the so-called Porolithon ridge has also been involved. It was found that in some places on the windward side of the reef more vigorously influenced by strong wave action, Porolithon ridge may occupy as much as 50-70% of the reef surface. In this respect, the role of corallinaceous algae in the reef formation in the Xisha Islands is very similar to that of the Marshall Islands (Taylor, 1950) and of the Solomon Islands (Womersley and Bailey, 1970).