A 24-year-old man presented with abdominal distension, diarrhea, and nausea. Blood tests showed eosinophilia (WBC 14400/microl, Eos 36%) and slight hypoproteinemia (TP 6.4 mg/dl, Alb 3.7 mg/dl). Ultrasonography and computed tomography revealed massive ascites (WBC 11500/microl, Eos 95%, protein 4.7 g/dl) and wall thickening of the small intestine. Endoscopic and histological examinations showed mucosal redness and edema with eosinophilic infiltration throughout the digestive tracts. Fecal alpha1- antitrypsin clearance was increased (44.6 ml/day). A diagnosis of eosinophilic gastroenteritis with ascites and protein-losing gastroenteropathy was made, and was classified as mixed type of both predominant subserosal and mucosal disease. Prednisolone therapy improved all the symptoms and findings. Measurements of serum levels of several cytokines and chemokines showed that interleukin-5 and soluble interleukin-2 receptor, but not eotaxin, were possible indicators of the disease activity. It should be kept in mind that eosinophilic gastroenteritis is one of the causes of ascites.