Acanthopanax sessiliflorus Seemann (Araliaceae) is a shrub and growing widely in Korea and China.Its root barks (Acanthopanacis Cortex) have been traditionally used as a tonic and a sedative,as well as in the treatment of rheumatism and diabetes.Many studies reported that this plant exhibits anti-oxidant,anti-inflammatory,anti-bacterial,anti-cancer,anti-hyperglycemic,anti-pyretic,immunostimulatory,hypocholestrolemic effects.[1] However,the memory enhancing effect of this plant has not yet been reported.Acanthopanacis Cortex was known to contain acanthosides A,B,C,D,daucosterol,several eleutherosides,β-sitosterol,stigmasterol,campesterol and (-)-sesamin etc.[2] As a part of our continuing search for new anti-amnesia agents from natural sources,we examined the memory enhancing effect of the root barks of Acanthopanax sessiliflorus 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 methylene chloride fraction among the samples tested significantly prevented the scopolamine-induced memory impairment in the passive avoidance and the water maze tests and properly inhibited the acetylcholinesterase activity.Among the isolated constituents,(-)-sesamin,a lignan compound,showed remarkable anti-acetylcholinesterase activity.