The distribution of the nucleolus organizer regions (NORs) on the chromosomes of 10 individuals of Bufo stejnegeri(Anura, Bufonidae) was investigated by conventional and NORs-staining analysis. 1. Seven individuals exhibit one pair of NORs on the long arm of the chromosome pair 6(standard form) 2. The one individual had a pericentric inversion on chromosome bearing NORs, whereby a large part of the NORs translocated in an telomeric position on the short arm. Therefore, a trace of original NORs remained an original terminal position on the long arm. Only one of the largest homologues had additional small NORs in the interstitial region of short arm. The possible explanation is the mechanism of translocation and segmentation (or fragmentation) in the NORs cluster(varied form I). 3. The two individuals exhibit inter- and intraindividual variation in number, position and size of the NORs. The mechanisms of these variation were explained by translocation and segmentation (or fragmentation) of NORs (varied form II).