Abstract: Objective To investigate the the effects of insulin-like growth factor 1 (IGF-1) on cognitive function in aged mice after microinjection of IGF-1. Methods IGF-1 was injected into the lateral ventricles of aged C57/BL6 mice. The expression of IGF-1R was assayed by Western Blot. The proliferative cells of the hippocampal dentate gyrus were marked by 5-bromodeoxyuridine (BrdU) immunofluorescence. The neurons of the hippocampal dentate gyrus were determined by Nissl staining. Morris water maze and step-down test were performed to evaluate the cognitive function of the aged mice. Results Western blot results showed that the protein level of IGF-1R increased in the IGF-1 treated group compared with the control group (P < 0.05). BrdU immunofluorescent results revealed BrdU-positive cells were obviously increased in the IGF-1 treated group compared to the control group (P < 0.05). Nissl staining revealed the increased number of neurons in the IGF-1 treated group compared with the control group (P < 0.05). Morris water maze test showed that escape latency of the IGF-1 treated group was significantly shorter than that of the control group after training, and the number of times through the platform was significantly larger than that of the control group (P < 0.05). Step-down test showed that the number of times of basal errors was dramatically smaller, and the latency was significantly longer in the IGF-1 treated group compared with the control group (P < 0.05). Conclusions After injection of IGF-1, the neurocognitive functions of aged mice were improved, so we may indicate that IGF-1 may improve the cognitive function in aged mice.