Heavy proteinuria in the nephrotic range is an uncommon, often unrecognized manifestation of graft-versus-host disease (GVHD) following hematopoietic stem cell transplantation. A few isolated case reports have been published in the Korean literature involving a small number of patients who developed membranous nephropathy as GVHD after peripheral blood stem cell transplantation (PBSCT). A 17-year-old female was diagnosed with non-Hodgkin's lymphoma. Following remission, she underwent allogeneic PBSCT. Shortly thereafter, she developed acute GVHD, which was managed by medical therapy with prednisolone and cyclosporine. Approximately 13 months following PBSCT, the patient developed proteinuria without peripheral edema. Pulsed steroid therapy was initiated three times, but her condition did not improve. Twenty months after PBSCT, she developed nephrotic range proteinuria. A renal biopsy was performed, and the diagnosis was histologically consistent with membranous nephropathy. Because the response to steroids was not satisfactory, the dose of cyclosporine was increased. Approximately 3 months after renal biopsy, the proteinuria disappeared. Given the recent increase in the incidence of GVHD-mediated renal disease, in particular, renal biopsy is indispensable to the diagnosis of nephropathy and to the prevention of disease progression.