A 42-year-old female complaining of fever and night sweats was diagnosed with acute megakaryoblastic blast phase chronic myeloid leukemia (CML-BP). She had massive splenomegaly, left pleural effusion with leukemia infiltration, and moderate myelofibrosis. She received dasatinib monotherapy (140 mg/day) as for induction, after which her pleural effusion rapidly resolved and hematological remission was achieved. However, CML relapsed 4 months after starting dasatinib due to increased BCR-ABL fusion signals in the peripheral blood. The T315I mutation was also detected at the recurrence of CML. As a salvage treatment, ponatinib monotherapy (45 mg/day) was started immediately. After 5 months, BCR-ABL fusion signals decreased to 5%, and myelofibrosis improved from MF Grade 2 to 1; she then underwent allogeneic bone marrow transplantation from an unrelated donor. However, the graft failed, and cord blood transplantation (CBT) was performed. Ponatinib (15 mg/day) was continued after CBT as a maintenance treatment, with molecular complete response continuing for more than 1 year with no severe adverse events, including cardiovascular events. There is limited evidence regarding the optimal dose and schedule of ponatinib before and after allogeneic hematopoietic stem cell transplantation, especially in patients with CML-BP having T315I mutation; thus, well-designed clinical trials are warranted.