The incidence of syphilitic aortic aneurysm was decreased now a day. The predilection site of cardiovascular syphilis is the thoracic aorta, especially ascending portion. The form of syphilitic aneurysm is characterized by saccular or fusiform. We have experienced 58 year old female complained of intermittent left chest pain for these 2 years. Saccular aneurysm of 7 cm in diameter at the descending thoracic aorta just distal to the left subclavian artery was confirmed with aortogram, and etiologic lesion was suspected as syphilis by her strong positive finding of serum VDRL test. Excision of the aneurysm was done under temporary bypass with heparinized 10mm silicone bypass cannula, and 23 mm Dacron aortic prosthetic graft in 10 cm segment was replaced, and excised aortic segment was confirmed as syphilitic aneurysm on light microscopic examination. Postoperative hospital course was uneventful, and discharged 3 weeks after operation in good normotensive condition. The patient died of CVA 3 months after discharge at home. [KTCS 1982;4:409-413]