Eosinophilic colitis (EC) is a rare disease which characterized by infiltration of eosinophil in colon and peripheral eosinophilia. Other causes of peripheral eosinophilia need to be excluded before assumed EC such as food allergy, inflammatory bowel disease, or parasites. It has bimodal distribution, peaked at neonates and young adult.A 24-year-old man was admitted with abdominal pain and chronic diarrhea. He has no any disease, food, pollen, or drug allergy in his medical history. Leukocyte: 29,000/mm3 (neutrophil: 43.4%, eosinophil: 44.4%, lymphocyte: 8.2%), platelet: 453,000/mm3, total eosinophil: 17,582.1/µL (normal range: 50-300), immunoglobulin E: 1000 IU/mL (normal range < 100 IU/mL) was counted in his blood examination. The colon biopsy was reported as eosinophilic colitis. We applied methylprednisolone 24 mg/day. With this treatment, the patient?s symptoms regressed.EC may involve any part of the gastrointestinal tract. An intense inflammatory infiltrate, consisting predominantly of eosinophils penetrates into one or more layers of the gastrointestinal tract. In 1937, Kaijser described this disorder. EC is classified into mucosal, submucosal or muscular, and serosal types. The endoscopic findings may vary from normal mucosa to frank ulceration. Our patient had chronic diarrhea and peripheral eosinophilia which are typical features of the mucosal types. It should be put in differential diagnosis in patients with chronic diarrhea.