Stress is known to influence the immune function via an effect on the central nervous system. To investigated the effects of Kwibitang water extract (KBT) on the specific immune response in C57BL/6 mice stressed by immobilization, we evaluated the changes in the cell viability, DNA fragmentation and subpopulation of thymocytes and splenocytes. KBT enhanced the cell viability of thymocytes and splenocytes decreased by immobilization stress. Also, KBT decreased DNA fragmentation of thymocytes and splenocytes increased by immobilization stress. KBT decreased the population of CD4⁺ cells and CD8⁺ cells in thymocytes and Thy1⁺ cells in splenocytes increased by immobolization stress, but increased the population of B220⁺ cells decreased by immobilization stress. In addition, KBT enhanced the production of ν-interferon and IL-2 decreased by immobilization stress. These results indicate that KBT may be useful for the prevention and treatment of stress via enhancement of the specific immune response