Sudden operative death due to massive tumor embolism occurred during operation. During the course of anesthesia for pneumonectomy, this 54-year-old male patients showed continuous hypotension, weak or absent pulse of radial, external carotid, femoral and doralis pedis artery of the right side. But those of the other side were within normal range and anesthesia went on uneventfully. As the patient failed to gain consciousness postoperatively, immediate emboleetomy under general anesthesia was performed under the impression of massive tumor embolism. Multiple tumor emboli were removed from the innominate arteries, right common carotid and right brachial artery. After operation of embolectomy, arterial blood pressure and pulse measured on the right side were regained. However, the patient failed to return to his consciousness and died due to unexpected cardiac arrest, 2 days later.