The purpose of this research was to investigate the effects of Bopaewon-tang (BT) on immune reaction in mice. BT (500 mg/kg, p.o.) increased the viability of thymocytes, but decreased the viability of splenocytes in vivo. BT enhanced the population of $CD4^+$cells in thymocytes and enhanced the population of $Thy1^+$ cells in splenocytes and splenic $CD8^+$ cells. Also, BT decreased the production of IL-4 from splenocytes. Furthermore, BT enhanced the production of nitric oxide and the phagocytic activity of peritoneal macrophages. These results suggest that BT enhances the immune response via activation of thymocytes and macrophages.