It is known that stress suppresses neurogenesis in the hippocampus. Neurotrophin-3 (NT-3), a neurotrophic factor, has been reported to be upregulated in the hippocampus of adult mice by stress and corticosterone administration. In order to investigate the effects of increased NT-3 on neurogenesis in the hippocampus and stress-induced behaviors, we generated NT-3 overexpressing mice in the hippocampus by administering adeno-associated virus carrying the NT-3 gene (AAV-NT-3). NT-3 mRNA was expressed more than 7 times higher in the hippocampus by AAV-NT-3 administration compared to control hippocampus. NT-3 expression was mainly localized in hippocampal hilus. After 4 weeks of AAV-NT-3 administration, the number of proliferating cells in the hippocampal dentate gyrus was decreased in the NT-3 overexpression group compared to the control group. This result suggests that high dose of NT-3 may suppress proliferation of neuronal stem cells/progenitors in the dentate gyrus. In the future, we plan to investigate changes in neural differentiation and maturation in the hippocampus of NT-3 overexpressing mice to further clarify the role of NT-3 in neurogenesis. It is also necessary to clarify the effects of NT-3 on stress by examining stress-induced anxiety-like and depression-like behaviors in NT-3 overexpressing mice.