A successfully-treated case of acute type B aortic dissection associated with a mycotic aneurysm is reported. A 69-year-old man had a history of febrile illness and a high CRP level with increased enzyme activity of the hepatobiliary system before the onset. The culture of the abscess in the distal arch aneurysm revealed Bacteroides fragilis. A Dacron graft replacement between the distal arch and the proximal descending aorta was successfully performed with Teflon felt reinforcement, and the graft was covered with omental flap. The patient was discharged without recurrence of infection 2 months after the graft replacement.