Some epidemiological studies revealed that the consumption of dairy products prevents cognitive decline in the elderly. We previously demonstrated that tryptophan-tyrosine (WY)-peptide rich in Camembert cheese suppresses microglial inflammation. In the present study, 7-week-old (young) and 68-week-old (aged) C57BL/6J mice were fed diet containing WY-peptide. After 4 months of feeding, mice were subjected to behavioral evaluations of the Y-maze test and the novel object recognition test (NORT), which were decreased in aged mice compared to young mice, but those in aged mice with WY-peptide were improved. The levels of pro-inflammatory cytokines and glutamate in the hippocampus of aged mice were higher compared to young mice, while they were decreased by WY-peptide. These results suggest that WY-peptide consumptions suppress microglial inflammation in the hippocampus, resulting in memory improvement. Aged mice orally given WY-peptide or whey peptide rich in WY-peptide for shorter term (18 days) also improved the memory impairment. The present study demonstrated that long-term or short-term consumption of WY-peptide is beneficial for age-related memory impairment.