Eosinophilic gastrointestinal disorder (EGID) is an uncommon disease that is accompanied by intestinal eosinophil infiltration without a secondary cause of eosinophilia. Eosinophilic enteritis is a secondary portion of EGID that can present a range of gastrointestinal symptoms according to the affected depth of the intestinal layer. The subserosal type of eosinophilic enteritis presenting as ascites is relatively rarer than the mucosal type. In general, eosinophilic enteritis occurs in patients with food allergies, but its mechanism is unclear. The authors experienced a 29-year-old female patient with a large amount of ascites with diarrhea and abdominal pain. The patient was diagnosed with an influenza A infection one week earlier. Peripheral eosinophilia (absolute eosinophil count: 6,351 cells/mm3) and eosinophilic ascites (97% of white blood cells in the ascites are eosinophil) were present. Abdominal CT revealed a large amount of ascites and edematous changes in the ileum and ascending colon wall. A diagnosis of eosinophilic enteritis was confirmed as eosinophilic ascites by paracentesis, with eosinophil infiltration of the bowel wall by an endoscopic biopsy. The patient´s symptoms improved rapidly after using steroids. To the best of the author´s knowledge, this is the first report of eosinophilic enteritis with massive ascites after an influenza A virus infection in a Korean adult.