Eosinophilic gastroenteritis is a rare condition of unknown etiology characterized by peripheral eosinophilia, eosinophilic infiltration of the gastrointestinal tract, and gastrointestinal symptoms. Eosinophilic gastroenteritis is generally classified according to the Klain classification: predominant mucosal, muscular, and subserosal disease. Mucosal involvement may result in abdominal pain, nausea, vomiting, diarrhea, weight loss, anemia, protein-losing enteropathy, and intestinal perforation. Patients with muscular layer disease generally have obstructive symptoms. Subserosal eosinophilic infiltration may result in development of eosinophilic ascites. Most commonly, the stomach, duodenum, and small bowel are involved. A 13-year-old girl came to our hospital presenting with chronic, intermittent abdominal pain. She showed peripheral eosinophilia and biopsy specimen of the duodenum revealed eosinophilic infiltration of the mucosal layer. We here report a case of eosinophilic gastroenteritis.