The Three months subacute toxicity of water soluble dimethyl dimethoxy biphenylate derivative (DDB-S), newly formulated therapeutic agent for hepatitis, was invesgated in SD rats. The body weight and clinical signs were observed after intravenous injection of DDBs at doses of 57, 75 and 100 mg/kg/day for three months. Decrease in motor activity and tremor were observed above 75mg/kg treated groups. Statistically significant changes at serum biochemical analysis were found in some group, how-ever, those changes were within the normal range and had no relationship with dosage. There was no abnormal morphological and pathological findings in relation to DDB-S treatment. The no observable adverse effect level of DDB-S in rats was estimated to be 57 mg/kg/day in this study.