The subacute oral toxicity of 1-(4-methylpiperazinyl)-3-phenylisoquinoline (CWJ- a-5) was investigated in Sprague-Dawley (SD) rats. Five groups of 5 males and 5 females were orally administered at doses of 0, 37.5, 75, 150 and 200 mg/kg with CWJ-a-5 for 2 weeks. In clinical signs, Salivation was observed in the 75, 150 and 500 mg/kg male and female groups. Loss of fur was observed in the 500 mg/kg male and female group. Body weight were significantly decreased in the 150 and 500 mg/kg male groups and in the 500 mg/kg female group. Food consumption was significantly decreased in the 300 mg/kg male group. In serum biochemistry, total cholesterol and phospholipid were significantly increased in 500 mg/kg male and female group. Aspartate aminotransferase was significantly increased in the 500 mg/kg female group. In histopathological examination, vacuolar degeneration of renal tubules in the kidney, vacuolar degeneration of hepatocytes in the liver vacuolar degeneration of myocytes in the heart, vacuolar degeneration of histiocytes in the spleen and thymus, atrophy of seminiferous tubule and degeneration of germinal epithelium in the testis, vacuolar degeneration of corpus luteum, granulosa cell and theca cell in the ovary were observed in the 150 and 500 mg/kg male and female groups. Based on these results, the no observed adverse effect level (NOAEL) with CWJ-a-5 was considered to be 75 mg/kg and the absolute toxic dose was considered to be 150 mg/kg in this study