Although the autogenous vein graft is the most reliable in the fields of microvascular reconstruction, the microvascular allograft and microvascular prosthesis have been developed to be substitute for autogenous vein because it has many problems. In many experimental study have been reported highly variable patency rate and its thrombogenetic property of microvascular allograft. Especially, antigenicity of the homogenous vessels and immune reaction-induced thrombosis are main cause of homogenous microvascular anastomosis failure. For that reason, several investigators have attempted to reduce the antigenicity and improve the patency rate of microvascular allograft. The purpose of this study was to observe the healing process in applying frozen arterial allograft in the rats. In order to perform this study, 27 Sprague-Dawley rats, weighing 300gm or more selected. 12 carotid arterial anastomoses were performed in the rats by using microvascular end-to-end anastomosis as control group and 15 frozen(-196degreesC) arterial allografts were implanted into the carotid artery in the rats by using microvascular anastomosis as experimental group. The experimental rats were sacrificed on the 1st, 3rd, 7th, 14th, 28th, 56th day after operations. For scanning electron microscopic study, fixation was performed by perfusion of 2.5% glutaraldehyed-2% paraformaldehyed in 0.1M phosphate buffer at pH7.3. The specimens were post-fixated in 1% osmium tetraoxide for 2 hours, washed with cacodylate buffer, dehydrated in a series of ascending ethanol baths, critical point dried, coated with gold in a vacuum evaporator, and observed with a scanning electron microscope(JEOL, JSM-840-A, 20kV). For histologic examination taken specimens were embedded in paraffin, sectioned 6-8micrometer in thickness. The specimens were stained with hematoxylin-eosin stain method, examined under light microscope. The results were as follows; 1. The patency rate of control group was 92% and experimental group was 86%. 2. Endothelial cells regeneration at the anastomosis site of both group was partially appeared on the 1st week after experiment. 3. On the 2nd week after experiment, anastomosis site was completely covered with regenerated endothelial cell in both group, and the endothelial cell proliferated toward the graft at experimental group. 4. On the 4th, 8th week after experiment, the grafted artery was partially covered with endothelial cell at experimental group.