We evaluated genetic diversity and differentiation among five wild populations of the swimming crab () using eight polymorphic microsatellite loci. We collected crabs from Zhoushan (ZS), Haizhou Bay (HZ), Huichang (HC), Laizhou Bay (LZ), and the mouth of the Yalu River (YL). We isolated 72 alleles from eight loci among the five populations. The number of alleles ranged from 6 to 12 and the average number of alleles () were 9.0 and 5.467 7, respectively. The mean PICvalue for the eight microsatellite loci was 0.696 7. The expected heterozygosity () of each population was as followsHZ (0.741 5), and ZS (0.728 3). The observed heterozygosity () was between 0.648 1 and 0.760 4. Six loci deviated significantly or very significantly from Hardy-Weinberg equilibrium. The genetic distances among populations ranged from 0.245 1 to 0.517 9. The UPGMA tree suggested that there were two different groups: one being composed of YL and LZ, and the other of HC, HZ and ZS. The values ranged from 0.054 8 to 0.108 3, suggesting that the degree of differentiation was moderate among the five wild populations (0.05<<0.15).