The sex chromosomes of Rana rugosa distributed widely in Japan were analyzed by the methods of conventional staining, C-banding and late replication (LR)-banding on 196 frogs consisting of 105 females and 91 males belonging to 24 populations of one group and three subgroups. The chromosome numbers of these frogs were all of 2n=26. The 12 pairs other than chromosome pair No. 7 had no sex differences in all the populations. In chromosome pair No. 7,sex-specific changes were found among some local populations. Seven populations belonging to the northern subgroup of the eastern group, including the Asahikawa and Sapporo populations in Hokkaido region, the Hirosaki, Akita and Inawashiro populations in Tohoku region, the Murakami and Kanazawa populations in Hokuriku region and the Katata population in Kinki region of the southern subgroup, had chromosome pair No. 7 which was the sex chromosomes of the ZW type. The Z chromosome was subtelo- or submetacentric, while the W chromosome was metacentric. By the C-banding and LR-banding patterns, the Z chromosome was divided into five types, Z^A, Z^B, Z^C, Z^D and Z^O, while the W chromosome was divided into two types, W^1 and W^2. Five populations of the southern subgroup of the eastern group, including the Toba population in Kinki region, and the Oigawa, Hamakita, Miyakoda and Yonezu populations in Chubu region,...