Objectives: The study was designed to evaluate the single dose toxicity of modified Bo-yang-Hwan-o-Tang (mBHT) in Sprague-Dawley (SD) rats. Methods: The mBHT was once administrated orally to both sexes of rats at dose 2,000 mg/kg body weight which are the recommended maximum limit dose for acute toxicity. We recorded clinical signs of toxicity, body weight, gross and histological changes in target organs for all rats. Results: Neither significant changes of body weight not death was observed during the observation period in mBHT-administrated rats. Neither significant toxic signs not histopathological changes were shown during the observation period. There were not observed significant gross abnormality between the control and mBHT-administrated rats. Conclusions: These results indicated that the toxicity of mBHT is greater than 2,000 mg/kg body weight in SD rats.