Partial sequence of the mitochondrial cytochrome b gene was analyzed to investigate the intra- and interspecific differentiation between 2 species of the genus Rana (R. nigromaculata and R. plancyi). The sequence of the 35-base pairs, which covers approximately 28% of the cytochrome b gene, was determined by PCR-direct silver sequencing method. The published sequence of Xenopus laevis was utilized for outgroup comparisons. The levels of mtDNA sequence differences were ranged from 0.3-2.9% within species, 3.8-6.4% between Rana species, and 24.1-17.9% between Rana species and Xenopus laevis. Transition was more frequent than transversion at synonymous sites. Transitions were dominated at the third position of the codon. In the amino acid analyses, 12 amino acid differences were found between Rana and X. laevis. Based on Tamura-Nei distance, percent sequence divergence was estimated 8.5% within Rana and 34.3% between Rana and X. laevis.