The pathway of nerves containing acetylcholinesterase (AChE) to the major cerebral arteries was investigated in the rat. In this species, the internal ethmoidal artery (IEA) arises from the anterior cerebral artery (ACA) and anastomoses with the external ethmoidal artery (EEA), forming the ethmoidal rete on the cribriform plate. The ethmoidal nerve (EN) and EEA enter the cranial cavity through the ethmoidal foramen. Densely distributed adventitial nerve plexi were present around the IEA, ethmoidal rete, and EEA. Many thick nerve bundles were found in the periadventitial layers in association with these vessels. Around the EN, just before it enters the ethmoid foramen, intensely staining nerve bundles were present that entered the cranial cavity with the EN. After unilateral section of the EN and EEA, a marked decrease of the nerve fibers was observed around the arteries of the anterior part of the circle of Willis on the operated side, whereas the basilar artery (BA) showed a moderate decrease in the AChE activity. After bilateral section of the EN and EEA, nerves disappeared from around all the major cerebral vessels including the BA. Section of the EEA alone did not produce any visible change of the cerebral perivascular innervation. The present study suggests that AChE-containing nerves on the cerebral arteries arise from the AChE-positive nerve bundles, which enter the cranial cavity with the EN through the ethmoid foramen; The anterior part of the circle of Willis is innervated unilaterally by the AChE-positive nerve bundles from the ethmoidal foramen, whereas the BA receives bilateral innervation.