Eosinophilic esophagitis has been reported as a complication of oral immunotherapy (OIT), but there are only a few reports of eosinophilic gastroenteritis (EGE) occurring after OIT. EGE causes eosinophil infiltration into the gastrointestinal (GI) tract and is characterized by various digestive symptoms. We report the case of a 6-year-old boy with EGE. He was diagnosed as having immediate-type food allergies (egg, milk and wheat) by oral food challenges at 1 year of age. OIT for each food was carried out, and the amounts of the offending foods were able to be gradually increased without causing any immediate-type allergy symptoms. However, the total IgE and specific IgE values were remarkably increased at the age of 4 years and 4 months. He first developed oral mucosa symptoms and vomiting at 4 years and 10 months of age, and they gradually worsened. Stopping eggs and milk alleviated the symptoms. Nevertheless, he still occasionally vomited. He started Pica eating disorder (sand and sponge) due to anemia from 5 years and 10 months of age and developed eosinophilia without diarrhea or bloody stool. Upper and lower GI tract endoscopic examinations found no bleeding. The GI mucosa showed eosinophil infiltration of more than 40/high-power field in the stomach and duodenum, so he was diagnosed with EGE. No eosinophils were found in the esophageal mucosa. His GI symptoms and anemia improved on a multiple-food-elimination diet. Patients undergoing OIT should be closely followed up for a long time, and those with GI symptoms should be evaluated by GI endoscopy.