Based on the complete psaA gene sequence of Phaeocystis antarctica in GenBank, two primers psaAL and psaAR were designed to amplify psaA gene sequence fragment of Phaeocystis globosa. An unambiguous sequence of 629 bp was gained,which was aligned with the complete psaA gene of Phaeocystis antarctica in Clustal X. The corresponding nucleotide dissimilarity of the two sequences was only 3.34%, and no insertion/ deletion was found. The relative amino acid sequence and RNA secondary structure were concluded in DNAstar． The concluded amino acid sequence was also conservative，and there was only one distinct base among 209 amino acids，with the difference of 0.48％ ．However，the concluded RNA secondary structures were quite unlike，apart from a few conservative domains． Perhaps the secondary structure of RNA may benefit the study on taxonomy of Phaeocysitis．It is considered that the DNA sequences and amino acid sequences of psaA are conservative, which is unadvisable to use for molecular interspecific classification ofthe genus Phaeocysitis.