Nucleic acids exhibit various biological functions, whereas their roles in the brain are largely unknown. We have recently reported that the ingestion of DNA hydrolysate derived from salmon milt improves cognitive function in healthy mice. However, effect of ingestion of RNA on cognitive function is still unknown. The purpose of the present study was to elucidate the effect on cognitive function and mechanisms of action of yeast-derived RNA (tyRNA) in mice. Seven-week-old ICR mice were fed a low-nucleic acid diet (AIN-93M) or that containing 2.5% tyRNA. Fourteen days later, the novel object recognition test (NORT) was performed to evaluate cognitive function. The exploration time for novel object was significantly longer than that for the familiar one in mice ingesting tyRNA, whereas the exploration time was not different between the novel and familiar objects in the control mice. Measurement of mono-nucleic acids by LC-MS/MS showed that concentrations of uridine, cytidine, UMP, and dCMP in the brain of tyRNA ingestion group were significantly higher than those in control group. Effect of exposure to uridine, cytidine, UMP, and dCMP on expression of Synapsin 1 (Syn1), a presynaptic marker in primary cultured murine cortical neurons was then evaluated by Western blotting. Only cytidine tended to increase Syn 1 expression compared to vehicle-treated group, suggesting that cytidine may promote synaptogenesis. Taken together, ingestion of tyRNA in mice increased several mono-nucleic acids including cytidine in the brain and improved cognitive function in mice.