The incidence of pulmonary thromboembolism after chest surgery is increasing. Five cases of it in recent two years were described. Four cases were lung cancer, and the other was myasthenia gravis. All lung cancer cases were after left lobectomy, and the findings of thromboembolism were mainly detected in right lung. Though hypocapnia is characteristic of pulmonary thromboembolism, arterial blood gas tests did not show it in all cases. Slight hypoxemia and arrhythmia are noteworthy signs of pulmonary thromboembolism after chest surgery. As thrombolytic and anticoagulation therapy, urokinase and heparin were very useful in four of five cases. Four patients made a rapid recovery from pulmonary thromboembolism, but one died of cerebral hemorrhagic infarction. The other patient did not recover in spite of intense medication, extracorporeal membrane oxygenation, and pulmonary embolectomy. To prevent pulmonary thromboembolism after chest surgery, appropriate countermeasures should be considered.