Genetic relationships among six species of the genus Rana from Korea were investigated by complete nucleotide sequence analyses of mitochondrial cytochrome b gene (1143 bp). Based on Kimura-2-parameter distance, the interspecific sequence differences of cytochrome b gene within the genus Rana were ranged from 7.83% to 25.00%. The genetic distances were 7.83% between R. nigromaculata and R. plancyi, 8.47% between two types of R. rugosa (type A and B), 10.42% between the brown frogs (R. amurensis and R. dybowskii), 16.11% between R. dybowskii types 1 and 2 and 12.36% between pond frogs (R. nigromaculata and R. plancyi) and R. catesbeiana. In the neighbor-joining and parsimony trees, R. catesbeiana was more closely related to pond frogs than brown frogs. R. dybowskii types 1 and 2 were considered to be at a distinct and specific level of differentiation (16.11%), while two types of R. rugosa were suspected to be at a subspecific level (8.47%).