The diameter of cerebral arteries play an important role in assessing the cerebral circulation flow as well as selected the size of the intravascular devices in the treatment of cerebral vascular intervention. Multislice computed tomography (MSCT 64) have a high sensitivity and specificity in evaluation cerebral arteries. The study was carried out to determine the diameters of all cerebral arteries parts forming the circle of cerebral artery on MSCT 64. The results showed that, the diameter of cerebral arteries range from 1.94 -2.94mm, minimum at communicating arteries and maximum at basilar artery. There was no significant difference between two sides of circle of Willis and genders. In conclusion,studies have initial determined the average size and variability of the diameter of cerebral arteries in Vietnamese population and their clinical significances.