1. Objectives This study was designed to andyze the acute toxicity and safety of Yeoldahanso-tang 2. Methods We investigated the acute toxicity for water-extracted Yeoldahanso-tang. 25 male and 25 female mice were observed for 14 days after one day oral administration of Yeoldahanso-tang at the respective doses of 0(control group), 2560, 3200, 4000 and 5000 mg/kg. 3. Results We observed survival rates, general toxicity, change of body weight and autopsy. 4. Conclusions The data confirmed that Yeoldahanso-tang is free from the toxicity and safety problems in oral route respectively. Compared with the control group, we could not find any toxic alteration in all treated groups(2560, 3200, 4000 and 5000 mg/kg). In conclusion, LD50 of Yeoldahanso-tang was over 5000 mg/kg and it is very safe to mice.