The chromosome constitutions of 106 individuals of Hynobius leechii collected from 17 localities in Korea were analyzed by Giemsa and Ag-NOR staining methods. The chromosome number of most of the individuals was 56 with AN number of 94. The size of NORs was homomorphic or heteromorphic pair at the tip of centromere of No. 23 chromosomes in 59 out of 106 individuals. The rest exhibited a high level of variation in number and site of NORs, but there was no intra-individual variation. All specimens from 4 (Hadong, Kurye, Chisan, Yangpyong) out of 17 populations had NORs on No. 23 chromosome, while many specimens from the rest of the populations had NORs variations with the rate of 44%. The mechanisms of NORs variation were explained by translocation and pericentric inversion of the parts of NORs, insertion of amplified 18S+28S rRNA gene segment and Ag-NOR staining effect that stain only real NORs in a species. Especially, all the specimens from Yangsan showed that the site of NORs was located at a little below the centromere on No. 23 chromosome, which caused by pericentric inversion.