We report an 85-year-old woman with rupture of aneurysm of the descending thoracic aorta into the left lung. She was admitted with sudden onset back pain and hemoptysis. Emergency operation was performed to replace the ruptured descending thoracic aorta, and lower lobectomy of left lung. The left lobectomy ensured that hematoma was not left in lung, although it decreased respiratory function after operation. In addition, it decreased bleeding and operating time compared to segmental resection. She was discharged without contracting an infection in the lung or graft, although she needed tracheotomy for a time. We suggest that the lower lobectomy of lung was an important factor in saving this elderly patient with rupture of an aneurysm into the left lung.