Eosinophilic gastroenteritis is a rare condition of unknown cause characterized by peripheral eosino-philia, eosinophilic infiltration of the gastrointestinal tract, and gastrointestinal symptomatology. Eosinophilic gastroenteritis is generally classified according to the layer of gastrointestinal tract involved. Especially, serosal eosinophilic infiltration is the rare,;t form of presentation, and may result in the development of eosinophilic ascites. Herein we repcrt an unusual case of eosinophilic gastroenteritis presenting with peritoneal eosinophilic infiltration diagnosed by a peritoneal biopsy. A 16-year-old woman came to our hospital presenting with abdminal listensiron and tenderness, vomiting, and diarrhea with marked peripheral eosinophilia. Stool .;pecimens were negative for ova parasites. Biopsy specimens of esophagus, stomach, duodenum, and colon showed nonspecific intlammation but that of the peritoneum showed specific intense e.inophilic infiltration with fibrous band and eosinophilic vasculitis. A diagnosis of serosal eosinophil c gastroenteritis based on clinical, laboratory, eosinophilic pertoneal fluid and histopathologic data, (:specially the biopsy specimens of the peritoneum. She was treated with corticosteroid and respond d dramatically with a complete resolution of ascites and other G-I symptoms.