Acase of unruptured cerebral aneurysm at the junction of accessory middle cerebral artery and the distal portion of the A1 segment of the anterior cerebral artery is reported. To the authors’ knowledge, this is the first reported case of cerebral aneurysm developed at the junction of accessory middle cerebral artery, demonstrated on magnetic resonance angiography(MRA). The accessory middle cerebral artery is a rare vascular variant of middle cerebral artery. Furthermore, it is extremely rare for an aneurysm to be developed at the origin of the accessory middle cerebral artery. The development of the accessory middle cerebral artery is very important in surgery of cerebral aneurysm and collateral circulation of cerebral infarction. Review of the literature regarding the genesis and anatomical variation of the accessory middle cerebral artery is also presented.