Drug-induced mental disturbances are frequent in bone marrow transplantation (BMT) patients who require numerous kinds of drugs. Although steroid-induced mental disorder is common in BMT settings, its treatment has not been fully investigated. We encountered a patient with acute myeloid leukemia who developed depressive disorder induced by steroid given for graft-versus-host disease treatment. Lithium carbonate was effective for the treatment of depressive disorder without causing side effects such as renal dysfunction. This study demonstrates the effectiveness of lithium carbonate for the treatment of depressive disorder induced by steroids in BMT settings.