Oral administration of a food-derived hydrophilic amino acid ergothioneine (ERGO) enhances memory function in mice at clinically achievable plasma concentration, although the mechanisms underlying the ERGO-induced cognitive enhancement remain unclear. We here tried to clarify the mechanisms using mice fed ERGO-free diet (ERGO-deficient mice). Hippocampal ERGO concentration in the ERGO-deficient mice was about 15 times lower than that in mice fed with normal diet. Oral administration of ERGO in ERGO-deficient mice enhanced learning and memory according to novel object and spatial recognition tests with a concomitant restoration of ERGO level in the hippocampus. To clarify the mechanisms, we focused on hippocampal neurogenesis induced by tropomyosin receptor kinases B (TrkB), one of the neurotrophin receptors. The oral ERGO administration increased area of a neurogenesis marker doublecortin-positive cells in the hippocampal dentate gyrus with a concomitant increase in protein expression of phosphorylated TrkB. In contrast, simultaneous administration of a TrkB inhibitor significantly suppressed the ERGO-induced cognitive enhancement and neurogenesis. These results suggest that the ERGO-induced cognitive enhancement would be caused by phosphorylation of TrkB and promotion of neurogenesis in the hippocampal dentate gyrus.