Chaga mushroom (Inonotus obliquus) has been identified to have various biological activities. This study was performed to investigate the potential of chaga mushroom as a immunomodulating functional food. When mouse splenocytes were exposed to various concentration of hot water extracts of chaga mushroom (IOE) with mitogens (Con A, LPS), splenocytes proliferation was significantly increased. Also, IFN-γ and IL-4 levels were significantly enhanced. Therefore, our results suggest that chaga mushroom may have the potential of being an immunomodulating functional food.