Abstract: AIM: To study the action of osthol(a constituent isolated from Fructus Cnidii) on learning and memory and its mechanism.METHODS: Step through test, step down test and Y-maze method were used to observe the effect of osthol on learning and memory. The duration of breath in beheaded mice, the content of the lipoperoxide(LPO) in the liver and brain of rats and the activity of acetylcholinesterase(AchE) were determined to analyze the mechanisms of action of osthol.RESULTS: Osthol was shown to improve impairment of memory acquistion, consolidation and direction discrimination. However, osthol did not show significant effect on impairment of memory retrieval. Osthol was found to prolong the duration of breath in beheaded mice, inhibit malondialdehyde(MDA)formation in the liver and brain of rats and decrease the AchE activity. Osthol was shown not to affect the sleep induced by sodium pentobarbital and the spontaneous activity of mice.CONCLUSION: Osthol can improve the leaning and memory of mice. The mechanism of action of osthol is considered to be related to inhibition of AchE activity and delay of cell ageing.