Two patients with malignant thymoma of lymphoepithelial cell type developed nephrotic syndrome and irreversible acute renal failure 18 months after the radiation therapy. Repeated renal biopsies revealed focal segmental glomerulosclerosis (FSGS) in both cases (a 66-year-old female and a 82-year-old female). Several immunological disorders were found, being a presence of autoantibodies such as antinuclear antibody, anti-acetylcholine receptor antibody, antistriatal antibody and an elevation of serum IgM. In both cases the nephrotic syndrome was resistant to corticosteroid as well as cyclophosphamide. Renal dysfunction eventually progressed to end-stage renal failure requiring regular hemodialysis treatment. A sustained immunological impairment related to the residual malignant thymoma was considered to be of pathogenic importance for the delayed occurrence of nephrotic syndrome. Fifteen thymoma cases with nephrotic syndrome from the previous reports are also reviewed.