The object of this study was to obtain acute information single oral dose toxicity of Mahwangbujaseshin-tang extracts, with mouse bone marrow cell micronucleus test for detecting possible genotoxicity. In order to observe the 50% lethal dose, approximate lethal dosage, maximum tolerance dosage and target organs, test articles were once orally administered to ICR mice at dose levels of 2000, 1000, 50 mg/kg according to the recommendation of KFDA Guidelines. The mortality and changes on body weight, clinical signs and gross observation were monitored during 14 days after dosing according to KFDA Guidelines with organ weights of 12 types of principle organs. In addition, after twice oral treatment of Mahwangbujaseshin-tang extracts 2000, 1000 and 500 mg/kg, we checked the changes on the number of MNPCE. We could not find any mortality, clinical signs, changes in the body weight and gross findings upto 2000 mg/kg treated group. The limited dosages in rodents except for increases of lymphoid organ weights and hypertrophy encounted as results from pharmacological effects of Mahwangbujaseshin-tang extracts, immune modulator effects with some sporadic accidental findings not toxicological signs. No evidence of increases of MNPCE numbers were also detected in all three different dosages of Mahwangbujaseshin-tang extracts treated mice. The results obtained in this study suggest that the LD50 and ALD of Mahwangbujaseshin-tang extracts in mice were considered as over 2000 mg/kg because no mortalities were detected upto 2000 mg/kg that was the highest dose recommended by KFDA and OECD. And the results of mouse bone marrow micronucleus test of Mahwangbujaseshin-tang extracts is negative results.