A 69-year-old woman presented with persistent dyspnea and continuous coughing and mediastinal mass. The mass was found to be a malignant thymoma and was resected incompletely. A full-blown nephrotic syndrome appeared 1 year after removal of the thymoma. Renal biopsy revealed minimal-change glomerulonephritis. There was no evidence of other autoimmune diseases or causes of the minimal-change glomerulonephritis.