A 38-year-old man was diagnosed with acute lymphoblastic leukemia. We performed myeloablative bone marrow transplantation from an unrelated donor during the patient's first complete remission. After engraftment, he developed acute graft-versus-host disease involving the gastrointestinal tract on day 32. Steroids and mycophenolate mofetil were initiated from day 39. His symptoms improved and the dose of immunosuppressants was tapered and then discontinued on day 421. On day 491, he developed nephrotic syndrome (NS). Based on renal biopsy, membranous nephropathy was diagnosed. There were no apparent symptoms or abnormal laboratory data suggestive of chronic graft-versus-host disease (cGVHD). Steroid therapy was initiated from day 518 and proteinuria improved significantly. NS is very rare following allogeneic hematopoietic stem cell transplantation (allo-HSCT). When there is no concomitant cGVHD, as in this case, allo-HSCT-associated NS is difficult to distinguish from idiopathic NS.