We report a case of spontaneous intraperitoneal hemorrhage from a ruptured mesenteric branch artery aneurysm in a patient presenting with syncope. A 54-year-old woman was brought to our emergency department as a medical code, following two syncopal episodes. Computed tomography, carried out to rule out aortic aneurysmal disease, revealed hemoperitoneum without evidence of solid organ injury. Emergency exploratory laparotomy revealed a large jejunal mesenteric hematoma accompanying a ruptured mesenteric branch artery aneurysm with active extravasation. We ligated and excised the lesion and diagnosis was confirmed on final pathologic examination. We report this case because general surgeons should be aware of these vascular lesions and the basic guidelines for treatment.