Food allergy is a disease caused by an abnormal immunological reaction to specific food proteins. Whole milk and soy beans are the most frequent causes of food allergy, some studies show that 2.2~2.8% of children aged between 1 and 2 year are allergic to milk. It can be classified to acute (urticaria, asthma, anaphylaxis) or chronic (diarrhea, atopic dermatitis) allergy according to clinical symptoms, or to IgE related or non IgE related allergy by an immunological aspect. Generally, allergies invading only the GI tract are mostly due to a non IgE related reaction. These hypersensitive, immunologic reactions of the GI tract, not related to specific IgE for food, present themselves in many ways such as food protein-induced enteropathy, food protein-induced enterocolitis syndrome (FPIES), celiac disease, food induced protocolitis, or allergic eosinophillic gastroenteritis. FPIES is one kind of non IgE related allergic reaction and is manifested as severe vomiting and diarrhea in infants between 1 week and 3 months. We report a case of FPIES in a 40-day old male infant presenting with 3 times of repeated events of watery diarrhea after cow's milk feeding.