Objective To illustrate the significance of lateral chiasmal arteries (LCAs) in visual disturbance caused by pituitary adenomas(PAs)，the microanatomical characteristics of LCAs were studied. Methods LCAs of 10 adult brain specimens，which were fixed with formalin and injected with colored mass，were observed and taken measure using microanatomical technique. Results LCAs arised from the medial wall of supraclinoid segment (CSUB>2/SUB> segment) of internal carotid artery (ICA). Each vessel ramified several twigs (from 2 to 3) into the lateral margin，superior and inferior aspects of the lateral part of the optic chiasma(OC)，and the lateral half of the optic nerve(ON) neighboring the OC. In summary，the perforating arteries with long free segments of the external brain took the form of chains or series of irregular loops，ran in the subarachnoid space and feed special areas. Their major trunks were not communicated each other during the course. But there were rich terminal anastomoses on the pial mater of the brain. Conclusion LCAs are not apt to being invaded by PAs，which might be the caus