OBJECTIVE: To investigate the effects of the Sini San at different doses on each sleeping state[slow-wave sleep 1(SWS1), slow-wave sleep 2(SWS2), rapid-eye-movement(REM), wakefulness(W)] in insomnia rats and to identify its mode of ac-tion for improving sleep.METHODS: The insomnia rats were randomly divided into a high-, medium- or low-dose group of Sini San(equal to crude drug 8.8, 4.4, or 2.2 g/kg, respectively) for seven consecutive days.RESULTS: Compared with pre-administration,SWS2 was significantly increased after administration of the low dose. Compared with pre-administration, W was significantly decreased and SWS1,SWS2, and the total sleeping time(TST) were markedly increased after administration of the medium dose. Compared with pre-administration, W was significantly decreased and SWS1, SWS2, rapid-eye-movement sleep, and TST were significantly longer after administration of the high dose. The effects of Sini San on sleep-wake cycle are dose-dependent.CONCLUSION: The results suggest that Sini San extends SWS1 and SWS2, which increases the total sleeping time.