Arterio enteric fistulas (AEFs) are rare. We herein report a case of a primary arterio enteric fistula of the rectum associated with Takayasu arteritis. A 77-year-old woman presented with acute massive hematochezia and was taken to our hospital. Colonoscopy revealed pulsatile extrinsic rectal wall compression with an exposed blood vessel. Transvaginal ultrasonography and Doppler ultrasound revealed a localized vascular growth laying on the dorsal surface of the uterus that showed an arterial blood-flow signal. We diagnosed the patient to have a pelvic aneurism that had formed a fistula within the rectal wall. We eliminated the aneurysm by ligating the drainage and feeder arteries. Following surgery, the patient did not experience any relapses of hematochezia.