Purpose : The purpose of this research was to investigate the effects of Kamibojoongikkitang (KBT) on the immune cells in C57BL/6 mice. Methods : KBT (500mg/kg) was administerd p.o. once a day for 7 days. Results : KBT decreased the cell viability of thymocytes in vivo and in vitro system and decreased the cell viability of splenocytes in vivo, but increased the viability of splenocytes in vitro system. In addition, KBT did not affect the population of helper T (Th) cells and cytotoxic T (Tc) cells in thymocytes and decreased the population of T- and B-lymphocytes and the population of Th and Tc cells in splenocytes. Furthermore, KBT did not affect the production of ${gamma}%-interferon and interleukin-4 in splenocytes. KBT increased the production of nitric oxide in vivo but decreased the production of nitric oxide in vitro system. KBT enhanced the phagocytic activity of peritoneal macrophages in vivo, but decreased the phagocytic activity in vitro. Conclusion : KBT has an inhibitory action on the specific immune response via decrease of the cell viability of thymocytes and splenocytes and has a potent action on the non-specific immunity via increase of phagocytic activity of peritoneal macrophages.