Purpose : This study was undertaken to observe the occurrence of the vessel aneurysms according to several different methods of microvascular anastomosis. Mterials & methods : Forty Sprague-Dawley rats, weighing $180{sim}200$ grams, were used for this experiment. The rats were divided into 4 groups. Group 1 (10 rats): The adventitia was trimmed off 5mm from the cut edge each and 20 arterial anastomoses were performed using 8 to 10 interrupted 9-0 polypropylene ($Prolene^{TM}$, Ethicon, U.K.) suture. Group 2 (10 rats): The adventitia was trimmed off as in group 1. Twenty arterial anastomoses were performed using continuous 9-0 polypropylene($Prolene^{TM}$, Ethicon, U.K.) suture. Group 3 (10 rats): The adventitia was stripped only 1mm from the cut edge each but not removed,. Twenty arterial anastomoses were performed using 8 to 10 interrupted 9-0 polypropylene($Prolene^{TM}$, Ethicon, U.K.) suture. Group 4 (10 rats): The adventitia was handled as in group 3. Twenty arterial anastomoses were performed using 9-0 polypropylene($Prolene^{TM}$, Ethicon, U.K.) suture. The arteries of the animals in all groups were explored at 28th days. We examined patency, presence of an aneurysm, other vascular abnormalities and microscopically observed the aneurysms with H&E and Van-Gieson stains. Result : 1. Patency rate was 80% in group 1, 95% in group 2, 85% in group 3 and 90% in group 4, respectively. 2. Aneurysm occurred 20% in group 1, 5% in group 2, 5% in group 3 and 5% in group 4, respectively. 3. There was no other vascular abnormalities in each group. 4. Infection rate was 5% in group 1, 0% in group 2, 20% in group 3 and 15% in group 4, respectively. 5. In the histopathological findings, we observed partially necrotic changes, loss and fragmentation of outer elastic lamella of smooth muscle in media and the proliferation of hyperplastic subintima. A lot of inflammatory cells were infiltrated in hyperplastic intima. Conclusions : On the basis of these observation, we could state that there were little differences in the occurrence of aneurysms according to different anastomotic suture methods.