Fifteen sequences from the mitochondrial cytochrome c oxidase subunit I gene （COI） were determined for 4 species of the genus Meretrix, with the homologous sequences ofM. petechialis obtained from the GenBank data library The alignment length of the sequences was 574bp after excluding ambiguous sites, including 93 parsimony informative sites. In the fragments, the percentages of A, T, C and G were 21.15%, 44.71%, 14.05% and 20.09% respectively. There were 12 haplotypes identified： 4 M. meretrix, 2 M. IamarckiL 3 M. lusoria, 1 M. lyrata and 2 M. petechialis. Furthermore, it was revealed that M.. meretrix, M. petechialis and M. lusoria shared some haplotypes. Phylogeny trees were reconstructed by Maximum-parsimony （MP） and Bayesian method using Qylina sinensis as the outgroup. Our results indicated that M. lusoria, M. petechialis and M. meretrix are closely related species. This is in accordance with the viewpoint that M. petechialis and M. lusoria should be treated as a junior synonym of M. meretrix.
