Eosinophilic gastroenteritis is a rare gastrointestinal disorder of undetermined etiology that is characterized by eosinophilic infiltration of the gut wall. The presenting symptoms depend on the site and depth of intestinal involvement and varies from nausea, vomiting, and abdominal pain to acute bowel obstruction. Pancreaticobiliary obstruction caused by eosinophilic gastroenteritis is rare. We report a 39-year-old man who presented with abdominal pain, vomiting, abnormal liver tests, and a duodenal mass on upper endoscopy. Blood tests showed peripheral eosinophilia. Abdominal computed tomography scan showed a suspected mass in ampullary region. At endoscopic retrograde cholangiopancreatography, both pancreatic and common bile duct were dilated with no obvious ductal strictures. Biopsies from the duodenal mass showed evidence of eosinophilic gastroenteritis. He was successfully treated with prednisone, and his liver test results returned to normal. In conclusion, this unusual case of eosinophilic gastroenteritis presented with duodenal mass that was masquerading as an ampullary adenoma causing pancreaticobiliary obstruction.