Thymoma is often accompanied by different paraneoplastic syndrome, such as myasthenia gravis, pure red-cell aplasia, systemic lupus erythematosus. Association of glomerulonephritis and thymic tumor is very rare, with only about 40 cases reported to date. The authors report here a case of nephrotic syndrome after thymectomy due to thymoma. A 68-year-old man presented with continuous coughing and mediastinal mass. The mass was found to be a thymoma of type AB and was resected completely. One month after removal of the thymoma, nephrotic syndrome appeared. Renal biopsy revealed diffuse foot process effacement, suggesting minimal change disease (MCD), with a focus of intraglomerular coagulation, suggesting thrombotic microangiopathy. There was no evidence of other autoimmune disease or causes of the nephropathy. Treatment with 500 mg methylprednisolone IV for three days followed by oral 60 mg prednisolone daily was started. After six weeks, his nephrotic syndrome was almost improved. To our knowledge, this is the second report of a patient with thymoma and MCD in Korea.