We report a patient with protein-losing gastropathy probably associated with autoimmune disease, in whom prednisolone treatment was highly effective. A 45-year-old woman was admitted to our hospital with edema of the face and lower extremities. Blood examination revealed hypoproteinemia, hypoalbuminemia, and hypercholesteremia. Renal biopsy revealed no definite findings of lupus nephritis, including vasculitis. A diagnosis of protein-losing gastropathy was made on the basis of increased alpha1-antitrypsin clearance and 99mTc-labeled human serum albumin scintigram showing abnormal radioactivity in the stomach. Endoscopic gastric biopsies revealed nonspecific inflammation, but marked intramural edema. Based on a slight elevation of antinuclear antibody level, autoimmune disease was suspected to be involved in this patient. Administration of prednisolone, as a diagnostic therapy, alleviated the hypoproteinemia, hypoalbuminemia, and hypercholesteremia. These findings suggest that an autoimmune mechanism could have been involved in this case of protein-losing gastropathy.