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.