Eosinophilic gastroenteritis (EGE) is a rare disease characterized by focal or diffuse eosinophilic infiltration of the gastrointestinal tract, especially the stomach and duodenum. EGE has vague, nonspecific symptoms, including nausea, vomiting, abdominal pain, diarrhea, weight loss, ascites, and malabsorption. Here, we report a patient with EGE presenting with concurrent acute pancreatitis and ascites. A 68-year-old woman was admitted with abdominal pain, nausea, vomiting, and watery diarrhea. Laboratory findings revealed elevated serum titers of amylase, lipase, and peripheral blood eosinophil count. An abdominopelvic computed tomography scan showed a normal pancreas, moderate amount of ascites, and duodenal thickening. A esophagogastroduodenoscopy showed patchy erythematous mucosal lesions in the 2nd portion of the duodenum. Biopsies from the duodenum indicated eosinophilic infiltration in the lamina propria. The patient was successfully treated with prednisolone and montelukast. Despite its unusual occurrence, EGE may be considered in the differential diagnosis of unexplained acute pancreatitis, especially in a patient with duodenal edema on imaging or peripheral eosinophilia.