Intraspecific differentiation of Rana tagoi was examined by electrophoretic analyses of 14 enzymes extracted from the skeletal muscles and livers and two blood proteins. A total of 194 Rana tagoi collected from seven stations in the western Japan had 22 loci controlling the enzymes and blood proteins. Of the 22 loci, those of AAT-A, AK and CK showed a single phenotype produced by a single allele. The other loci showed 2∿25 phenotypes produced by 2∿10 alleles. At the 22 loci, there were 6.9 phenotypes produced by 4.3 alleles on the average. The gene frequencies in the seven populations were examined at 19 of the 22 loci, except three loci of AAT-A, AK and CK, which consisted of a single allele. While these three loci were zero in Fst, five of the others were 0.015∿0.068,four were 0.144∿0.208,three were 0.312∿0.377,three were 0.423∿0.462,three were 0.516∿0.621 and the remaining Hb locus was 1.000 in Fst. Of the seven populations, the three island populations, the Yaku, Hirado and Oki populations, were lower in average heterozygosity than the other four land populations, the Nabara, Kurama, Omogo and Ono populations. The proportions of polymorphic loci in the seven populations were 40.9∿63.6%, 55.20n the average. The mean numbers of alleles per locus in the seven populations were 1.6∿2.5,2.0 on the average. The genetic distances among the seven populations were estimated on the basis of gene frequencies at the 22 loci. The largest distance (0.335) was found between the Yaku and Omogo populations, while the smallest (0.031) was found between the Nabara and Omogo populations. A dendrogram was drawn by the UPGMA clustering method. This dendrogram seems to indicate that the Yaku population (Rana tagoi yakushimensis) was differentiated earlier than the other six populations.