Pedicled omentoplasty is effective in thoracic surgery, but it is associated with several postoperative complications. A case of diaphragmatic hernia as a complication of pedicled omentoplasty in a 65-year-old male is reported. Because aortoesophageal fistula occurred three months after the patch aortoplasty for mycotic aneurysm of descending thoracic aorta, he underwent ascending thoracic aorta to abdominal aorta bypass surgery with resection of thoracic aortic aneurysm and esophagorrhaphy with wrapping of the esophageal suture line and the stumps of aorta with pedicled omental flap. Three years after the operation, herniation of the stomach developed. The pedicled omental flap was ligated and divided, and the diaphragm defect was repaired.