A 77-year-old man diagnosed with primary myelofibrosis (PMF), successfully controlled by thalidomide and prednisolone, was referred to us for massive subcutaneous bleeding involving the face, body, and all four limbs. Hemostatic studies showed prolonged activated partial thromboplastin time, decreased factor VIII coagulation, and a high factor VIII inhibitor titer, resulting in a diagnosis of acquired hemophilia A (AHA) for which he was treated with prednisolone and cyclophosphamide on admission. He developed right femoral intramuscular hemorrhage soon after immunosuppressive therapy and was treated with rituximab combined with activated prothrombin complex concentrates. Furthermore, he suffered complications of respiratory failure with increasing throat hemorrhaging. Recombinant activated factor VII (rFVIIa) was administered combined with methylprednisolone pulse therapy. Bleeding, including respiratory failure, was ameliorated with rFVIIa. Immunosuppressive rituximab therapy resolved AHA with marked efficacy. He died of Pneumocystis jiroveci pneumonitis. Autopsy showed transformation from PMF to acute myeloid leukemia.