AIM:To study the chemical constituents and their anti-amnesic effect from the hooks of Uncaria rhynchophylla.METHODS:The isolation of compounds was performed by chromatographic techniques and their structures were identified on the basis of spectral analysis.Their ameliorating effects on scopolamine-induced memory impairment in vivo using a Morris water-maze task and passive avoidance task system were evaluated.RESULTS:Activity-guided fractionation of the total extracts resulted in the isolation of four constituents,trans-anethole(1),p-anisaldehyde(2),estragole(3),and 3-oxo-olean-12-en-28-oic acid(4),which were found for the first time from this plant.CONCLUSION:Compound 1 exhibited a better memory enhancing effect than tacrine,a positive agent,at the same dose in the passive avoidance test and a similar property in the water-maze test,and its action may be mediated,in part,by the acetylcholine enhancing cholinergic nervous system.