Disclosed is an intestinal immune system stimulator which can stimulate an intestinal immune system effectively and is safe. ?-Glutamylcysteine is used as an active ingredient of an intestinal immune system stimulator which can be used as a medicinal agent for the treatment or prevention of infectious diseases, diarrhea, polyps, tumors, enteritis or allergy. A food having an intestinal immune system-stimulating activity can be produced by adding ?-glutamylcysteine to a food.
