We investigated the immunostimulatory effects of doenjang, a famous Korean traditional food made from fermented soybean paste, on the immunohistochemical reaction in the gastrointestinal (GI) tract and immune response in mice. Male C57BL/6N mice (6 weeks-old) were divided into 4 experimental diet treatment groups and a basal diet (control) group, and fed with different diets for 4 weeks. The immunoreactive density of $CD4^+/CD8^+$ lymphocytes were strongly stained in the jejunum and colon in Group III. The immunoreactivity of universal nitric oxide synthase (uNOS) was strongly stained in the myenteric plexus in the colon of all doenjang-fedgroups (I, II and III). The colonic immunoreactive density of protein kinase C-${alpha}$ (PKC-${alpha}$) was strongly increased in Groups II and III, while that of stem-cell factor (c-kit) was increased in colonic mucosa of all doenjang-fedgroups (I, II and III) and especially increased in the colonic muscle layer of Group III. These morphological and immunological results indicated that the intake of doenjang could improve the mucosal immune reaction, gastrointestinal motility, blood circulation in the GI tract, and the immuneactivity of the body. These results provide experimental evidence about the health benefits of doenjang.