Objective:To study the effect of Liuwei Dihuang Wan on aged rats with the learning memory and cholinergic M1 receptor(M1-AchR) positive neurons. Method: The SD rats were divided into three groups: healthy young control group(3 month-old﹚

the natural aging model group (24 month-old﹚and the Liuwei Dihuang Wan group(24 month-old﹚. Liuwei Dihuang Wan group and the natural aging model group were orally administered with Liuwei Dihuang Wan(3 g·kg-1﹚and the same volume of distilled water for thirty days;the healthy young control group was administered with the same volume of distilled water for seven days. It tested the learning and memory capacity with Morris water maze. It detected M1-AchR with immunohistochemistry. Result: All of the indexes between rats in older group and the healthy young control group were significant(P<0.01).The average escape latency of the elderly was significantly shorter than the Liuwei Dihuang Wan group since the third day

and there was a significant difference(P<0.01). Space exploration experiments showed that there was a significant difference between rats in older group and Liuwei Dihuang Wan group in the number of crossing the platform (P<0.01). Compared with the aged rats in control group

the numbers of M1-AchR positive cell of aged rats in Liuwei Dihuang Wan group increased in the hippocampus CA3 and primary somatosensory cortex; trunk region(S1Tr)

and there were very significant between them (P<0.01). Conclusion: Liuwei Dihuang Wan can improve the learning and memory of the natural aging rats

which was caused possibly by protecting M1 AchR positive neurons in the hippocampal CA3 and S1Tr and enhanced the central cholinergic system function.