Green soybean (Glycine max L.), which was used in this study, retains the green color of the seed coat cotyledon even after ripening, even though many soybean cultivars become yellow during maturation. We have reported that ingestion of green soybean extract (GSE) suppressed cognitive dysfunction and reduced amyloid β accumulation more than yellow soybean extract (YSE) in aged senescence-accelerated (SAMP10) mice, a mouse model of brain senescence. To clarify the mechanism by which GSE suppresses cognitive dysfunction, we examined the effect of GSE and YSE on neurite outgrowth in human neuroblastoma SHSY-5Y cells. GSE significantly increased cell number and neurite outgrowth at 5 ng/ml (as isoflavones, 30 pg/ml), but the effect of YSE was lower than that of GSE. Although isoflavone aglycones, genistein and daidzein increased the number of SH-SY5Y cells, the effect was only observed at a high concentration [0.05 μM (13 ng/ml)]. ICR mice were fed a diet containing 3% soybean extract for 3 weeks (3-4 g/kg; as isoflavones, ca. 20 mg/kg) to examine cognitive function. Learning and memory abilities, as evaluated by a step-through passive avoidance task, a Y-maze and a novel object recognition test, were significantly higher in mice that ingested GSE than control mice that were fed a normal diet. The expression of brain-derived neurotrophic factor (BDNF) in the hippocampus, as detected by western blot analysis, was higher in mice that ingested GSE than in control mice. This study suggests that the ingestion of GSE enhances learning and memory abilities in mice. The effect by which GSE improved cognitive function appears to be caused, in part, by increased neuritogenesis and BDNF expression.