To investigated the effects of Kwibi-tang water extract (KBT) on the non-specific immune response in C57BL/6 mice stressed by immobilization, we evaluated the changes in the contents of serum histamine and corticosterone and the phagocytic activity of macrophages. The level of serum histamine and corticosterone was determined with spectrofluorometer. The cell viability was determined by a MTT assay method. The subpolpulation of lymphocytes was determined by a flow cytometry. The phagocytic activity was determined with luminometer. KBT decreased the serum level of histamine and corticosterone increased by immobilization stress. Also, KBT enhanced the phagocytic activity and decreased the level of nitric oxde in murine peritoneal macrophages decreased by immobilization stress. These results indicate that KBT may be useful for the prevention and treatment of stress via suppression of serum histamine and corticosterone level and enhancement of the non-specific immune response.