Isozyme analysis on 40 populations of Hyla japonica and H. suweonensis from Korea and Japan was performed to survey their geographic distribution and to estimate the degrees of genic variation and diversity. A sum of 28 loci were screened from 22 enzymes and other proteins. The result showed that the genic variation of Ulsan population of H. japonica was the highest (Ho =0.146, He = 0.138) whereas Cheonan population of H. suweonensis was the lowest (Ho =0.036, He = 0.042). The average genic variation of H. japonica (Ho=0.107, He=0.121) is more than twice as high as that of H. suwonensis(Ho=0.048, He=0.047). The average genetic similarities among the populations in each species of H. japonica and H. suweonensis were very close as S=0.920 and S=0.967 respectively. However, in H. japonica, the average genetic similarity coefficients between Korean populations and Japanese population is lower (S=0.828) than average conspecific levels. The survey of geographic distribution of two sibling species, using the genetic markers (Aco, αGpd, Mdh-1, Sdh, Est-2, Mpi) shoed that H. japonica was widely distributed in Korea whereas H. suweonensis was restricted to a part of central region in Korea.