Soy (Glycine max, family Leguminosae) contains isoflavones and saponins as main constituents. In our preliminary study, soybean ethanol extract (SE) ameliorated scopolamine-induced memory impairment in mice in the passive avoidance task. Therefore, to confirm its ameliorating effect for memory impairments, we measured its effect in scopolamine-induced memory-impaired mice in Morris water maze task. SE significantly prevented scopolamine-induced memory impairment in the Morris water maze task. SE also increased the swimming time within quadrant section of the platform on the day after the final training session test. SE protected the reduction of brain-derived neurotrophic factor (BDNF) expression and cAMP response element-binding protein (CREB) phosphorylation in the hippocampi of scopolamine-treated mice. However, SE did not inhibit acetylcholinesterase. To understand the possible role of soysaponins in memory impairments, we prepared soyasaponins-rich (butanol) fraction of soybean (SRF) and investigated its protective effect against in the passive avoidance and Morris water maze tasks. SRF ameliorated scopolamine-induced memory impairment in mice. The memory impairment-ameliorating effect of SRF was more effective than that of SE. Based on these findings, soybean may improve memory impairment by regulating CREB phosphorylation and BDNF expression.