Eosinophilic gastroenteritis (EG) is characterized by eosinophilic infiltration of the bowel wall and variable gastrointestinal manifestations. Clinicians should have a high index of suspicion for EG when faced with gastrointestinal symptoms and peripheral eosinophilia to avoid incorrect diagnosis and inappropriate treatments. A 24-year-old woman was admitted to our hospital complaining of acute right lower quadrant abdominal pain and a laparoscopic appendectomy performed for a presumed diagnosis of an acute appendicitis. However, the procedure revealed bowel edema and a moderate amount of ascites without evidence of a suppurative appendicitis. Postoperatively, she showed persistent and progressive eosinophilia, exudative eosinophilic ascites, eosinophilic infiltration of the resected appendix wall, and eosinophilic infiltration of gastroduodenal mucosa. A punch biopsy of the abdominal skin also revealed inflammation with marked eosinophilic infiltration of the skin. She recovered after the treatment with a low dose of steroid for the EG with eosinophilic dermatitis. EG with eosinophilic dermatitis has not been reported yet and is considered fortuitous in this case.