Secondary aortoenteric fistula is a rare yet fatal complication after reconstructive surgery of aortic aneurysm. A 68-year-old man with a significant past medical history of type 2 diabetes, coronary artery disease status post cardiac stent, and aortobifemoral bypass graft performed 10 years ago, presented with shortness of breath, chills, and progressive anemia for the past 14 months. Patient reported one episode of melena 2 weeks before admission. The initial blood cultures growth of a variety of microorganisms (Streptococcus sanguis, Lactobacillus paracasei, Candida lusitaniae) and the subsequent blood cultures growth of another microorganism (Enterobacter Cloacae) were considered to have a GI source. A contrast CT scan of abdomen and pelvis did not show acute intra-abdominal process. Then a FDG PET-CT scan result showed hypermetabolism signal associated with the proximal end of the aortoiliac graft, concerning for infection of the graft itself. An esophagogastroduodenoscopy revealed a large centrally bulging lesion, without bleeding, in the third part of the duodenum, which was consistent with a secondary aorto-enteric fistula formed by infected aortic graft eroding into duodenum. The patient subsequently underwent explantation of the infected aortobifemoral bypass graft, reconstruction with cryopreserved aortoiliac allograft, and resection of small intestine with anastomosis closure of duodenotomy. The patient was discharged from the hospital 10 days after the operation and later was doing well. Secondary AEF should be suspected in patients presenting with unclear source of bacteremia with or without GI bleeding and a history of aortic repair. Clinical suspicion is the most crucial factor contributing to the right diagnosis.