Partial sequences of the mitochondrial 16S rRNA gene were determined for two Sesarma species （S. haematocheir and S. pficata）, and the length of sequence of S. haematocheir and S. plicata was the same. Of the 533 nucleotides obtained, the A, T, G and C contents were similar, which were 198 bp （37.1%）, 206 bp （38.6%）, 84 bp （15.8%）, 45 bp （8.4%） and 200 bp （37.5%）, 205 bp （38.5%）, 81 bp （15.2%）, 47 bp （8.8%） respectively. There were 49 different sites between the two species, including 21 transition sites, 22 transversion sites and 6 deletion/insertion sites. Furthermore, 361 bp homologous fragment was analyzed to discuss the phylogenetic relationship of 20 Sesarma species. The results showed that AT content （78.6% - 82.9%） was higher than GC content and there were 91 vadable positions of 16S rRNA sequences among the 20 species. Among 3 Sesarma species in China, S. dehaani and S. haematocheir were closely related （d=0.0151）; and there were greater genetic distances between S. pficata and S. dehaani I S. haematocheir （d=0.0924/0.0923）. The average genetic distances of S. plicata , S. dehaani and S. haematocheir with the North American crabs of genus Sesarma were respectively 0.103 2 ± 0.008 9, 0.0783±0.0105 and 0.072 0± 0.011, which indicated that there were greater genetic differences between China and North American Sesarma crabs and they were monophyletic each other.
