A 68-year-old man who was subjected to stent-grafting of a descending thoracic aortic aneurysm (TAA) 4 months previously was admitted to our hospital with constitutional symptoms, including high fever, sweating, nausea, vomiting, weight loss, and backache. An infected aneurysmal sac was suspected based on computed tomography (CT) findings, and an aortoesophageal fistula (AEF) was identified during esophagoscopy. CT-guided aspiration was performed using a 20-G Chiba needle, confirming the presence of infection. For treatment of the infected aneurysmal sac, CT-guided percutaneous catheter drainage in a prone position was performed under general anesthesia with left endobronchial intubation. Drainage catheter insertion was successfully performed using the Seldinger technique, which is not a standard treatment of an infected aneurysmal sac. Improvement in the patient's clinical condition was observed at follow-ups, and CT showed total regression of the collection in the aneurysmal sac.