Portunus triuberbuculatus is an important economical species in China. In recent years, the wild stocks of P.triuberbuculatus along the coast of China have suffered fatal decrease in their resources due to the overfishing and cultivation. So it is very important to investigate the genetic diversity of P.triuberbuculatus. In October 2005, 48 individuals were collected from Zhoushan Gulf. Muscle was collected from each of the samples and stored at -70 ℃ for detection. Muscle was homogenized in mercaptoethanol buffer(0.05%) at a ratio of 1∶3 (g·mL-1) with ice-bath and centrifuged at 12 000 r·min-1 for 30 min , 4 ℃. The supernatant was used as the isozyme source and electrophoresis was carried out on vertical polyacrylamide gels in Tris-gly buffer system (TG, pH 8.3) at 280 V for approximately 6 h at 4 ℃. The isozymes were analyzed by specific isozyme staining methods. The genetic variation was analyzed in terms of their locus number, structure, alleles, etc. Results showed that there were 20 loci by detecting eleven isozymes in this study. Among the scored loci, 4 loci (Me-2,Sod-3,Cat-3,Ldh-2) were polymorphic and the mean proportion of polymorphic loci (P) was 20%. The mean effective number of alleles per locus (Ae) was 1.230, and the mean expected heterozygosity per locus (He) and the mean observed heterozygosity (Ho) were 0.094 and 0.175, respectively. In the mean time, the deviation indexes from Hardy-Weinberg equilibrium (d) of four polymorphic loci (Me-2,Sod-3,Cat-3,Ldh-2) were analyzed with 1.000, 1.000, 0.818 and 0.333, respectively. The genetic variability of Portunus trituberculatus was higher than those of Eriochier japonica, Eriochier sinensis. 22 Refs.In Chinese.