Somatic chromosomes of two representative species of genus Hynobius were observed with the intestinal epithelium by the method of Kezer and Sessions (1979). Diploid number of H. n. nebulosus and H. naevlus was confirmed to have 56, which is an uniform number with other majority of species in genus Hynobius. Twenty-eight pairs of homologues were classified into four groups to facilitate the comparison of each karyoytpe. The chromosome morphology constituting both karyotypes was similar in general but not identical with each other. An unambiguous difference occurred in the mediumsized chromosomes (Nos. 10-13). Onsequently it brought about the different fundamental number (FN) between two species, 90 for H. n. nebulosus and 92 for H. naevius.
The karyotype of H. n. nebulosus, which is a common species and is widely distributed in western Japan, was not exactly the same with that analyzed by the previous workers. The minor difference found in the small-sized chromosome groups (Nos. 14-18 & 19-28) may indicated a chromosomal polymorphism according to the locality.