We have already reported that the D-Fraction, a β-glucan extracted from the fruiting body of the maitake mushroom (Grifola frondosa), activates cellular immunity and expresses anti-tumor effects. In this study we investigated the anti-tumor functions of D-Fraction in relation to its control of the balance between T lymphocyte subsets Th-1 and Th-2. D-Fraction decreased the activation of B cells and potentiated the activation of helper T cells, resulting in enhanced cellular immunity. It also induced the production of interferon (IFN)-γ, interleukin (IL)-12 p70, and IL-18 by whole spleen cells and lymph node cells, but suppressed that of IL-4. These results suggest that D-Fraction establishes Th-1 dominance which induces cellular immunity in the population that was Th-2 dominant due to carcinoma.