Objective: To observe the effect of urapidil (agonist of 5-HT 1A receptor ) on morphine withdrawal syndrome Method: A physical dependent model in mice was established by subcutaneous injection of quantitative morphine The intensity of withdrawal syndrome was evaluated by observing jumping latency, jumping times and lose of body weight after intraperitoneal injection of naloxone (5 mg/kg) The effect of urapidil was observed after intraperitoneal injection it with 3 different dosages (100, 200, 400 mg/kg) Contents of NO in plasma and brain tissue were measured by nitrate reduction method Results: Morphine withdrawal syndrome was inhibited by urapidil at any dosage Content of NO in brain tissue reduced by urapidil 400 mg/kg, while plasma NO increased Conclusion: Urapidil inhibits morphine withdrawal syndrome in mice, increase the content of NO in their brain tissue