Abstract： Objective Studying the difference of the uhrastructures of the internal elastic laminae (IEL)of the eommonal carotid artery among young,adult and aged rats in order to set up a efficient preventional and therapeutical strategies to the cerebrovascular disease(common diseases of the cerebral vessels)among aged people.Methods Twenty-four male Wistar rats,aged from 3 months to 3 yeam were used for this study.The IEL in the bifurcation of the right common caotide artery was isolated and digested with hot alkali.The luminal surface of each IEL was scanned by the scanning electric microscope.The number and the area of each fenestration in the IEL were measured and compared among three different age groups.Results The number of the fenestrations was the most in the adult(964.00±4.13),which was significantly more than that in the young(710.00±1.22)or in the aged group(624.00±2.54,P<0.01).The difference of the number of the fenestrations was not significant between aged and young rats(P>0.05).The number of the large fenestrations was remarkable increase with age increasing and the difference between any two groups was all significant[adult(52.40±2.79),young(13.00±1.10),aged(105.20±8.78),P<0.01].The mean percantage area of the fenestrations was also remarkably increasing with age[adult(23.58±2.12),young(15.52±1.70),aged(39.86±3.51),P<0.01].This value was the highest in aged rats which were significantly more than that in the aduh or in the young rats and the difference between adult and young groups was not significant.Conclusions The age-related decrease in elasticity and in the ablitity of preventing penetration of the macromolecules in the IEL maybe a crucial reason for higher incidents of atheroscelerosis and aneunynoma in the bifurcations in the common carotid artery in aged people.