Objective: The purpose of this study was to investigate the effects of Kamikwiryongtang (KKT) on the immune response and growth in a young mouse (3 weeks mice). Methods The viability of thymocytes and splenocytes in vivo and in vitro system, the population of helper T (Th) cells and cytotoxic T (Tc) cells in thymocytes and increased the population of T-lymphocytes and the population of Th cells in splenocytes, the production of ${gamma}$ -interferon, interleukin-2 and interleukin-4 in splenocytes was investigated. KKT (500mg/kg) was administerd p.o. once a day for 7 days. Results: KKT increased the viability of thymocytes and splenocytes in vivo, but did not affect the viability of thymocytes and enhanced the viability of splenocytes in vitro system. In addition, KKT did not affect the population of helper T (Th) cells and cytotoxic T (Tc) cells in thymocytes and increased the population of T -lymphocytes and the population of Th cells in splenocytes. Also, KKT increased the production of ${gamma}$-interferon, interleukin-2 and interleukin-4 in splenocytes. Furthermore, KKT increased the production of nitric oxide in vivo, but did not affect the production of nitric oxide in vitro system. KKT enhanced the phagocytic activity of peritoneal macrophages in vivo, but decreased the phagocytic activity in vitro system: KKT increased the body weight of a young mouse. Conclusions: KKT stimulates the specific immune response via increase of, the viability of thymocytes and splenocytes and the non-specific immune response via increase of phagocytic activity of peritoneal macrophages and stimulates the growth of a young mouse.