The genetic diversity and differentiation of 6 mud crab Scylla serrata populations from southeastern China are investigated using allozyme electrophoresis. The mean number of alleles per locus population is 1.3 ± 0.1; the percentage of polymorphic loci per population is 27.3; the observed heterozygosity ranges from ( 0.195 ± 0.083)to ( 0.241 ± 0.090) and the expected heterozygosity ranges from ( 0.105 ± 0.043 ) to ( 0.131 ± 0.047 ). The coefficient of gene differentiation among populations is low (Fst =0.032), indicating that only 3.2 % of the total genetic diversity comes from inter-population, while the remaining 96.8 % comes from intra-population differences.The genetic distance among populations is 0.000～0.008 (the average is 0.002). Gene flow among the populations is large (Nm= 7.56).Genetic structure is very similar among 6 Scylla serrata populations.