The experiment was designed to investigate the effect of magnesium on learning and memory ability in aged mice. Forty aged mice (14 months old) were divided into two groups randomly, magnesium-treated group and control group. In magnesium-treated group, mice were fed with the MgCl2 solution (concentration of solution: 4 mmol/L, dose: 10 mg/kg) for 60 days and then subjected to the novel object recognition test and passive avoidance task. No significant difference was found in locomotor activity and exploration between two groups. However, in the novel object recognition test, magnesium-treated mice showed significantly higher exploratory preference to the novel object than controls. In addition, compared to the controls, magnesium-treated mice exhibited longer escape latency in the passive avoidance test, suggesting that magnesium-treated mice have better fear memory. These results indicate that magnesium can improve the ability of learning and memory in aged mice.