Abstract: The phylogenetic relationship of six marine crabs was studied using random amplified polymorphic DNA (RAPD) technique.Predetermined optimal reaction conditions were as follows:Samples were first heated at 94℃ for 4 min;and followed by 45 cycles of 1 min at 94℃,1 min at 36℃,and 2 min at 72℃ then held at 72℃ for 10 min.With 16 primers,123 reproducible amplified fragments ranging between 500 and 14 000 bp were acquired.In all bands,2 bands were shared by all crabs,13 shared by Charybdis japonica,C.Acuta and C.Feriatus,16 shared by Portunus sanguinolentus and P.Trituberculatus.The amplified fragments were scored as present (1) or absent (0) for each DNA sample and an index of degree of band sharing (F) was calculated by using Nei and Lis matching coefficient method.The degree of F was 0.0606-0.8000.The value of 1-F was used to evaluate genetic distances between species.The genetic distances between species were 0.2000-0.9394.The phylogenetic trees were constructed with the method of UPGMA and NJ on the basis of genetic distances.The results from the two methods of cluster analysis are similar in general,and the relationships indicated by the phylogenetic trees show the difference between genus species.The results are in good overall agreement with classical taxonomy.