Gastrointestinal duplication cysts are rare congenital anomalies. Pyloric duplication represents 2.2% of all gastrointestinal tract duplications. The presentations merely depend on the site of occurrence, size and type of the cyst, and presence of ectopic mucosal lining. A ten years old girl vomited for two months, accompanied with stomach ache and difficulty in defecation. The color of stool sometimes was black. The body weight decreased twelve kilograms in two months. On physical examination, no abdominal distention and no palpable mass was found, bowel sound was decreased and there was tenderness in epigastric area. Nutritional status of patient was severe malnutrition. Laboratory test revealed mild hypochromic microcytic anemia, severe hyponatremia, severe hypokalemia, and hypoalbuminemia. Abdominal ultrasound revealed thickening of the gastric wall and upper gastrointestinal contrast study revealed partial stenosis with thickening of pyloric wall. Esophagogastroduodenoscopy revealed multiple gastric ulcers and gastric outlet obstruction. Cyst duplication and stricture in the pylorus were found during surgical procedure. The pediatric surgeon performed an excision of duplication cyst and gastroduodenostomy side to side anastomosis. Histopathologic examination from cyst confirmed the enteric duplication cyst. The patient was discharged in good condition. We concluded that pyloric duplication is considered as one of the differential diagnosis in children with symptoms of gastric outlet obstruction. Appropriate surgical procedures should be undertaken to avoid complications.