Abstract:Alexandrium tamarense was a wide-spread species of dinoflagellate causing harmful algal blooms and paralytic shellfish poisoning around the world. The genetic diversity of 5 European and 4 Chinese strains of A. tamarense was analyzed by using microsatellite markers. Relative low genetic diversity was revealed in the 9 strains of A. tamarense, with effective number of alleles of 1.3243~3.2667 and gene diversity of 0.3630. Based on the markers, the 9 strains of A. tamarense were divided into three lineages with genetic differentiation of 0.7522, which related to their geographic origins. Chinese samples could be divided into two lineages, and the European strains belong to another lineage. High genetic differentiation among the three populations suggested the lack of gene flow.