A 52-year-old male with complaints of pain and cold sensation on left upper-extremity was admitted to a hospital. He was diagnosed with acute left brachial artery occlusion and accordingly underwent emergency thrombectomy. Contrast-enhanced computed tomography (CT) revealed an ascending aortic mural thrombus (AMT). After his transferring to our institution, the AMT was removed, and the ascending aorta was replaced under cardiac arrest. Based on histopathological findings, the thrombus was caused by the destruction of an atheromatous plaque. The patient's postoperative course was uneventful, and no recurrence of AMT was presented for 12 months after operation.