The cholinergic M1 muscarinic receptors in brains of aged rats and the regulation effects of ZM （Anemarrhena asphodeloicles Bunge） and its sapogenine ZMS were studied with autoradiography of 3H-pirenzepine. The mean grain densities in different brain areas were estimated by a computerized image-analysis system. The specific bindings of aged rats were decreased by 15% in cerebral cortex and striatum and by nearly 10% in hippocampus. Parallel experiments showed that chronic daily oral administration of ZM or its sapogenine ZMS to aged rats can attenuate the decrease of M1 receptor densities of the above three areas and keep them nearly normal for a long time.