It is recommened to remove the arterial adventitia from the vessel ends to prevent adventitial interpose between the edges of anastomoses vessels. We have analysed the effect of adventitial removal on the patency in microvascular anastomosis. using rat femoral artery Three groups of adventitial removal methods were studied: non-removal group, sharp dissection group and blunt dissecction group. Patency was evaluated one hour, 24hours and 7days after anastomosis. The patency rate of non-dissection group(n=40) was 90% one hour after anastomosis but it reduced to 62.5% both at 24 hours and at 7days because interpositioning of adventitia induced thrombosis. The blunt skipping group showed 62.5% of patency rate at one hour most likely due to vascular spasm, but after 24hours it was recovered to 80% and 78.5% at 7th day. The sharp dissection group showed persistently high patency rate of 97.5% after one hour,95% both after 24 hours and after 7 days. Scanning electron microscopy showed endothelial loss and medial edema in bluntly stripped vessels but it showed well preserved endothelial cells and medial wall in sharp dissection group. The reason of relatively low patency rates of blunt dissection group compared with sharp dissection group 24 hours and 7 days after anastomosis(p=0.043 and p=0.023, respectively) was endothelial damage induced by stretching force made during blunt stripping.