Clean Natural is a new disinfectant of which main components are propolis and wood vinegar from Quercus mongolica. The mutagenicity of Clean Natural was studied by a micronucleus test in male ICR mice. The maximally tolerated dose (MTI) of Clean Natural was determined to >2.0 g/kg body weight. Therefore, the doses adopted for the micronucleus test was 2.0 g/kg as a high dose, 1.0 g/kg as a medium and 0.5 g/kg as a low of dose, respectively. Each of group was consisted of three doses of Clean Natural, positive control 2 mg/kg of mitomycin C and negative control 20 ml/kg of saline. A slide preparation was made at 24 hours following administration. No significant induction of micronuclei was observed in any of the three doses of Clean Natural orally administered. No cytotoxicity such as inhibition of hemopoiesis was observed in any group of test agent as the rate of polychromatic erythrocytes to total erythrocytes was over 40%. These results indicate that Clean Natural is not capable of inducing micronuclei in vivo mouse cells and thus has no genotoxicity in micronucleus test.