The root extract of Pulsatilla koreana (Ranunculaceae) has been found to have prominent abilities to reverse scopolamine-induced cognitive impairment in rats, and to increase the viability of human neuroblastoma SK-N-SH cells incubated with amyloid-beta peptide (1 - 42) [A beta (1 - 42)]. In vivo and in vitro activity-guided fractionation studies using solvent-partitioning and subsequent chromatographic separations led to the isolation of hederacolchiside-E, an oleanolic glycoside, as an active ingredient. Administration of hederacolchiside-E (30 and 60 mg/kg body weight, P. O.) increased the step-through latency time in the passive avoidance test as efficiently as tacrine (30 mg/kg, P. O.). The neuroprotective effect of hederacolchiside-E on SK-N-SH cells against the toxicity of A beta (1 - 42) was comparable to that of catechin. These data suggest that hederacolchiside-E might be a good therapeutic candidate for the treatment of Alzheimer's disease.