A 50-year-old male presented with left lower abdominal pain, visible pulsation below xiphoid process, and tenderness in the left iliac fossa for the past 10 days. Chest X-ray revealed blunting of left cardiophrenic angle. Echocardiogram revealed descending thoracic aortic pseudoaneurysm. Contrast-enhanced computed tomography of the chest and abdomen revealed dissecting aneurysm of lower thoracic and upper abdominal aorta. Thoracoabdominal aortogram revealed erosion of D12 vertebra and infected aneurysm of adjacent thoracoabdominal aorta. Serum venereal disease research laboratory assay was positive in 1:4 dilution Treponema pallidum hemagglutination assay was positive. The patient was treated with Injection procaine penicillin for 20 days undercover of steroids. Cerebrospinal fluid analysis was normal. Aortic aneurysm repair with reconstruction was done. Histopathology was in favor of syphilitic etiology. This case is being presented as descending thoracic and upper abdominal aortic aneurysm due to syphilis complicated by dissection and erosion of vertebral body is rare and has not been reported nowadays to the best of our knowledge.