Transverse myelitis is an inflammatory disorder of the spinal cord that results in motor, sensory, and autonomic dysfunction. Herein, we describe a 40-year-old Japanese female who developed acute transverse myelitis (ATM) after an unrelated bone marrow transplantation for Philadelphia-positive acute lymphoblastic leukemia in molecular complete remission. Approximately 90 days after transplantation, she suffered from paresthesias, sphincter dysfunction, and lower extremity weakness. Spinal cord magnetic resonance imaging scan demonstrated findings consistent with ATM. The symptoms were resolved with the administration of steroids, followed by intravenous immunoglobulin therapy for a few sequelae. To the best of our knowledge, the presentation of ATM after hematopoietic stem cell transplantation is relatively rare. As the functional prognosis of ATM depends on prompt diagnosis and treatment, we consider that ATM should be included in the differential diagnosis of post-transplant myelopathies.