In this study, the effect of daidzin or daidzein isolated from Pueraria lobata on the memory impairments induced by scopolamine was assessed in male mice using the passive avoidance and the Morris water maze tasks. Administration of daidzin (5 mg/kg) or daidzein (5 mg/kg) significantly reversed the scopolamine (1 mg/kg)-induced cognitive impairments in male mice as evidenced by the passive avoidance test (p < 0.05) and on the Morris water maze test (p < 0.05). Moreover, the ameliorating effects of daidzin or daidzein were antagonized by tamoxifen (1 mg/kg), the nonspecific estrogen receptor antagonist. These results indicate that daidzin or daidzein may be useful in cognitive impairment induced by cholinergic dysfunction, and this beneficial effect is mediated, in part, via estrogen receptor.