Late replication and C-banding analyses of somatic metaphase chromosomes were attempted on three species of brown frogs with 2n = 26 chromosomes (Rana japonica, R. tsushimensis and R. temporaria), and three with 2n = 24 chromosomes (R. ornativentris, R. dybowskii and R. chensinensis), which are distributed in the Palearctic region. The late replication banding patterns were highly conserved in these species. Four chromosome inversions were demonstrated in R. ornativentris, two in R. dybowskii and two in R. tsushimensis. From a detailed comparison of late replication and C-banding patterns between the 2n = 26 and the 2n --24 species, it was found that an end-to-end fusion of two small chromosomes (nos 11 and 13) in an ancestral 2n = 26 species may have produced the medium-sized no. 6 chromosome of the 2n = 24 species. Key words. Brown frogs; 2n = 24; 2n = 26; late replication band; C-band; an end-to-end fusion.