Kamikaekyuk-tang(KMKKT), a formula of ten Oriental herbs, was orientally designed to promote vital energy, to remove blood stasis, and to decrease inflammation for treating cancers. KMKKT and its component had potent antiandrogen and androgen receptor activities in prostate cancer and also inhibited angiogenesis induced by basic fibroblast growth factor (bFGF) in human umbilical vein endothelial cells and suppressed the tumor growth in LLC-bearing mice, and liver metastasis of colon 26-L5 cancer cells, suggesting a potent cancer preventive agent. Nevertheless, there is no safety study of KMKKT before clinical trial so far. Thus, in the current study, we investigated the toxicity about ethanol-extracted KMKKT. Male and female Spraque Dawley (SD) rats were given orally by KMKKT at 250, 500, and 1000 mg/kg for 4 weeks. Mortality, clinical signs and measured change of body weight, food consumption and water consumption were observed. In addition, we performed ophthalmologic, urinary, hematological, blood serum biochemical and histopathological examination. Any general toxicity was not found in KMKKT treated group. Also, there were no significant differences in the parameters such as body weight, food consumption and water consumption, a lot of urine and blood factor levels except WBC, MCHC and Ca level compared with control group. Although WBC and MCHC were elevated in female rats and Ca level was decreased in male rats, these were within normal ranges. Finally, we determined that maximum tolerated dose (MTD) was 1000 mg/kg and no observed adverse effect level (NOAEL) was 500 mg/kg. Taken together, these results demonstrated that KMKKT is very safe to SD rats.