In this study, the micronucleus test with peripheral blood using acridine orange coated slides was evaluated in mice treated with mitomycin C(MMC) at doses of 0.5, 1.0 and 1.5 mg/kg body weight. The peripheral bloods were obtained at 0, 24, 48 and 72h after treatment. The frequencies of micronucleated reficulocytes(MNRET) in the MMC-treated groups increased dose-dependently, and showed a peak time at 48h after treatment. We also performed the sex differences of MNRET frequency in 0.5 mg/kg MMC treated group, and we observed no sex differences in this experiment. And we evaluated the usefulness of a direct acting clastogen, N-methyl-N-nitrosourea and a indirect acting clastogen, benzo(a) pyrene as the positive control in this supravital micronucleus test. They also caused a significant increase in MNRET frequencies. These results suggest that the supravital staining micronucleus test using MNRET can be useful tool to evalulate the quantitative and qualitative assessment of genotoxicity in vivo compared to classical in vivo micronucleus test using bone-marrow cells.