Genetic variation of four strains of Meretrix meretrix, thin checkered(TC),black spot(BS),dark fringe(DF)and red shell(RS)was studied.Thirty randomly selected individuals from each strain and nine polymorphic microsatellite loci were used for genetic analysis.A total of 105 alleles were identified, the most alleles were 21(WG07)and the least locus were 7(WG11).The distribution of the alleles for the same loci was different in different strains and specific allele types were detected in each strains.All the microsatellites were highly polymorphic,and various genetic variability measures,including observed heterozygosity(0.486 to 0.867), expected heterozygosity(0.110 to 1.000), and polymorphism information content(0.433 to 0.834),Chi-square tests showed that most of the cases in four strains deviated from Hardy-Weinberg equilibrium.Pairwise F_ST ranged from 0.005 to 0.269.Genetic distances among strains ranged from 0.052 0 to 0.098 0.The results of cluster analysis indicated that TC strain had higher genetic difference than other strains,then was BS strain,and the genetic variation between DF and RS strains was relatively lower.