We retrospectively evaluated the efficacy of mycophenolate mofetil (MMF) in the treatment of steroid-resistant acute and chronic graft-versus-host disease (GVHD) after hematopoietic stem cell transplantation. Thirteen patients, ten men and three women, consisted of 5 cases of acute myelogenous leukemia, 2 of acute lymphoblastic leukemia, 2 of chronic myelogenous leukemia, 2 of lymphoblastic lymphoma, and 1 case each of adult T-cell leukemia and peripheral T-cell lymphoma. The transfusions consisted of 5 peripheral blood, 7 bone marrow and 1 cord blood from 3 mothers, 4 siblings and 6 unrelated donors with conditioning treatments, including 8 total-body irradiation-based regimens, and 2 busulfan plus cyclophosphamide and 2 reduced-intensity regimens. GVHD prophylaxis included FK506 plus methotrexate (MTX) and/or antithymocyte globulin for 9 patients, and cyclosporine and MTX for 4 patients. All patients were treated with second-line MMF for steroid-refractory acute and/or chronic GVHD, and 11 patients improved. The adverse events were tolerable except for one patient in whom grade 3 neutropenia forced discontinuation of treatment. No case of non-relapse mortality occurred. We consider that MMF is beneficial and well tolerated for treatment of steroid-refractory GVHD.