Uncaria rhynchophylla (Rubiaceae) is a woody plant and widely distributed in China and other East Asia.Its hooks (Ramulus Uncariae et Uncus) have been used for hypertension,infantile convulsion,and so on in oriental traditional medicine.This plant was reported to have antioxidant actions such as free radical scavenging effect and anti-lipid peroxidation activity and anticonvulsion property.[1]Although Choto-san,a Japanese Kampo medicine containing Chotoko (hooks of U.rhynchophylla) as the main component herb,was effective in the treatment of vascular dementia and also showed a protective effect against ischemia-induced cognition impairment in mice [1],the extracts and fractions of the hooks of U.rhynchophylla alone have not yet been investigated for ameliorating effect on scopolamine-induced memory impairment and also for anti-acetylcholinesterase activity.The hooks of U.rhynchophylla have known to contain some phenolic compounds such as epicatechin,caffeic acid,and quercetin.As a part of our continuing search for new anti-amnesia agents from natural sources,we examined the memory enhancing effect of the hooks of U.rhynchophylla by determinations of acetylcholinesterase inhibitory activity in vitro,passive avoidance task and Morris water maze task in animal models.The present study demonstrates the extraction,activity-guided fractionation,isolation of active constituents and in vitro/in vivo assays.As a result,the ethylacetate fraction among the samples tested significantly prevented the scopolamine-induced memory impairment in the passive avoidance and the water maze tasks and inhibited markedly the acetylcholinesterase activity.Among the isolated constituents,quercetin and epicatechin,which are well-known phenolic compounds,increased the step-through latency and reduced the escape latency in mice and showed strong anti-acetylcholinesterase activity.