We operated on 3 patients with thoracic or thoracoabdominal aneurysm using partial cardiopulmonary bypass with right atrial drainage. The first patient was in the preshock state with severe chest and back pain. The aortography and enhanced computed tomography showed a thoracic aneurysm of 70 mm in maximum diameter ruptured into the extrapleural space and an emergency surgery was performed. The second patient was also in the preshock state with chest and back pain. The enhanced computed tomography showed a thoracoabdominal aneurysm of 120 mm in maximum diameter ruptured into the bilateral pleural spaces and an emergency surgery was performed. The third patient had a thoracoabdominal aneurysm of 60 mm in maximum diameter with a low pulmonary function. In all 3 cases, a perfusion cannula was inserted in the femoral artery and a drainage cannula was placed in the right atrium through the femoral vein. In the first case, an additional perfusion cannula was inserted into the axillary artery in order to secure the cerebral flow even at the time of intraoperative massive bleeding from the aneurysm. In all 3 cases, the approach for aneurysm was through spiral incision and aneurysms were replaced by graft inclusion technique. All 3 patients had an uneventful postoperative course and are doing well. In surgical treatment of thoracic and thoracoabdominal aneurysm, usefulness of partial cardiopulmonary bypass using right atrial drainage was discussed.