In this research, the genotoxic effects of Kong-Jin-Dan(KJD), a polyherbal formula were evaluated using the mouse micronucleus test. KJD was administered once a day for 2 continuous days by oral gavage to male ICR mice at doses of 2000, 1000 and 500 mg/kg. Cyclophosphamide was used as a known genotoxic agent in a positive control. The appearance of a micronucleus is used as an index for genotoxic potential. In addition, the changes on the total white blood cells and differential counts on the lymphocytes, neutrophils, eosinophils, basophils and monocytes in the prepared blood smears were also conducted to observe the possible immunosuppress. The results obtained indicated that KJD shows no genotoxicity effects up to 2000 mg/kg dosing levels, but KJD shows slight increased trends in the blood total leukocyte numbers as pharmacological effects of immune stimulation. In addition, it is also considered that there were no problems from cytotoxicity of KJD tested in this study because the polychromatic erythrocyte ratio was detected as > 0.42 in all tested groups.