The prognosis of patients with relapsed osteosarcoma is dismal despite the use of intensive chemotherapy. We describe a patient with refractory osteosarcoma who underwent non-myeloablative peripheral blood stem cell transplantation (PBSCT) from an human leukocyte antigen (HLA)-identical sibling during a third complete remission. The patient suffered pulmonary relapse after the transplantation. Cyclosporin A withdrawal induced a graft-vs.-osteosarcoma effect and graft-vs.-host disease, but eventually the tumor progressed. Although our experience in this case suggested the presence of a graft-vs.-osteosarcoma effect during non-myeloablative allogenic PBSCT, this strategy might have limited value for refractory osteosarcoma with rapid growth kinetics.