Examination of sleep-inducing effect of Melatonin, through direct sleep-inducing test and the test of sleep-inducing in coordination with pentobarbitone in mice revealed that, oral low doses of Melatonin (0.083,0.5,3.0mg/kg BW) potentiated pentobarbitone-inducing sleep, and that higher dose (800mg/kg BW) had direct sleep-inducing effect, the sleep time is 70.8 minutes, sleep latency is 35.7 minutes. Author's address Zhou Yuhong, Institute of Food Safety Control and Inspection, the Ministry of Public Health of PRC, Beijing 100021, PRC.