Acute disseminated intravascular coagulation (DIC) is a rare complication of aortic aneurysm with or without dissection. We describe an 88-year-old man who presented with severe hemorrhagic diathesis and a pulsating abdominal mass. An abdominal computed tomography (CT) scan revealed a dissecting abdominal aortic aneurysm with thrombus formation, and his coagulation profile showed the features of acute DIC. After he had received blood component therapy, including fresh frozen plasma and cryoprecipitate concentrates, and intravenous heparin infusion (10,000 U/day), the bleeding diathesis and coagulopathy improved. An aneurysmectomy was performed smoothly without excessive bleeding. Coagulation parameters returned to normal after surgery. Dissecting aortic aneurysm should be considered as a possible etiology of acute disseminated intravascular coagulation, even it occurs in rare situations. Surgical intervention is still the main strategy to normalize coagulopathy. Bleeding diathesis must be corrected before surgery in order to prevent massive intraoperative bleeding.