A rare case of mycotic aneurysms of descending thoracic aorta is presented. A 63-year-old man was admitted with history of persistent high fever and loss of consciousness to our hospital. On admission, there were elevated WBC and CRP. Blood and spinal fluid cultures revealed growth of Streptococcus pneumonia. Despite of antibiotic therapy for meningitis and bacteremia, inflammatory sign continued, and new abnormal shadow appeared on chest X-ray. Chest CT and aortography showed two aneurysms of descending thoracic aorta. In an emergency operation, there was no abscess formation around the aneurysms. Aneurysms were excised en bloc without opening aneurysms followed by in situ Dacron tube graft replacement. The patient has been doing well without infection.