It is well known that Brain derived neurotrophic factor (BDNF) is a one of neurotrophic factors and a key player for sustaining of homeostasis in brain. On the contrary, there are few reports whether BDNF affects immune cells. We previously reported that BDNF affects immune cells and induced regulatory T cells (Treg). In this study, we investigated whether BDNF has effects on immune cells in vivo. At 24 hours after the BDNF administration by i.n., splenocytes were prepared. Flow cytometry demonstrated that BDNF administration induced Foxp3 positive cells in splenocytes. To determine whether BDNF administration affected splenocytes, proliferation of splenocytes were examined. The proliferation of splenocytes stimulated with mitogen (LPS) was attenuated. Additionally, TNF-α production induced by LPS was lower than control in splenocytes. These results suggested that BDNF contributes immune suppressive event in vivo.