Effect of quinolinedione derivative (OQ-21) on phenylephrine induced vasoconstriction was investigated using aortic rings in organ bath isolated from rats. Treatment with OQ-21 resulted in moderate increase in vasoconstriction in a dose-dependent manner. In addition we studied acute intraperitoneal toxicity of OQ-21 in male and female ICR mice. The changes of body weight and clinical signs were observed for 7 days after single dose of OQ-21 from 50 mg/kg to 500 mg/kg. There were no significant changes in body weight and clinical signs. Any mouse didn't die even at maximal dose. Autopsy of OQ-21 treated mice revealed no abnormal difference from contol mice, These results suggest that OQ-21 be moderately safe and could be developed as effective drug.