The toxic algae phaeocystis is one of key taxa in redtide-caused marine algae,due to its complex heteromorphic life cycle,great geograPhic differences,and minuteness of Polymorphic motile cells,the identification of Phaeocystis species is difficult and controversial.In 1997 and 1999,Pltaeocystis bloomed in southern China coastal waters,its taxonomic status is unresolved yet.The Partial sequence of 18S rDNA from the strain P₂ collected In Hong Kong coastal waters were determined in this study.The sequences were then used as molecular criteria to investigate the algae identities.The result shows that the strain is Phaeocystis globosa.