In this study, we investigated the effects of Inula Britannica on the production of antibodies against ovalbumin, and the differentiation of T cells, in C57BL/6 mice. The oral administration of Inula Britannica suppressed IL-4 and IL-6 production in lymphocytes collected from an inguinal lymph node in the immunized leg. On the other hand, the intraperitoneal administration of Inula Britannica suppressed IgG1 production, the ratio of IFN-gamma+IL-4-/IFN-gamma-IL-4+ cells and cytokine production of IL-6. It was presumed that the effects of Inula Britannica on the production of antibodies were induced by regulation of the balance of Th1 and Th2. Further, IL-4 and IL-6 production by lymphocytes collected from an inguinal lymph node in the immunized leg were suppressed, and therefore production of antibodies was suppressed.