Genomic DNA isolated from two species of Korean freshwater crab(Eriocheir sinensis) and swimming crab(Portunus trituberculatus) was amplified several times by PCR reactions. The seven arbitrarily selected primers OPA-05, OPA-13, OPA-16, OPB-06, OPB-15, OPB-17 and OPD-10 were used to generate the identical, polymorphic, and specific fragments. 505 fragments were identified in the freshwater crab species, and 513 in the swimming crab from Buan: 81 specific fragments(16.0%) in the freshwater crab species and 100(19.5%) in the swimming crab. 165 identical fragments, with an average of 23.6 per primer, were observed in the freshwater crab species. 66 fragments, with an average of 9.4 per primer, were identified in the swimming crab species. The numbers of polymorphic fragments in the freshwater crab and swimming crab were 50 and 14, respectively. The oligonucleotides decamer primer OPB-17 generated identical DNA fragments, approximately 300 bp, in both the freshwater crab and swimming crab species. Compared separately, the average genetic difference was higher in the swimming crab than in the freshwater crab species. The average genetic difference was $0.726{\pm}0.004$ between the freshwater crab and swimming crab species. The dendrogram obtained by the seven primers indicates four genetic clusters: cluster 1(FRESHWATER 01), cluster 2(FRESHWATER 02, 03, 04, 05 and 06), cluster 3(FRESHWATER 07, 08, 09, 10 and 11), and cluster 4(SWIMMING 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 and 22). The shortest genetic distance displaying significant molecular difference was between individuals SWIMMING no. 18 and SWIMMING no. 17 from swimming crab(0.096). Ultimately, individual no. 02 of the freshwater crab was most distantly related to freshwater crab no. 03(genetic distance = 0.770). As stated above, the potential of RAPD-PCR to identify diagnostic markers for the identification of two crab species has been demonstrated.