Microfibrillar Collagen(MFC) a effetive topical hemostatic agent, may be a highly effective embolic materialwhich has availability, ease of use through catheter and potent thrombogenicity, and causes occlusion at the levelof the arterioles leading to extensive tissue infarction, but is not widely used due to early recanalization ofthe vessels embolized and to known granulomatous arteritis. The author designed an animal experiment ontransarterial embolization using MFC for the patients with hemorrhage, malignant lesion, etc, in whichpreoperative vascular occlusion is desirable. Transcatheter embolization with MFC suspension was performed inright renal arteries of 22 rabbits. Post-embolization angiography, gross morphologic and microscopic examinationsof the kidneys embolized were evaluated 2 days, 1 week and 4 weeks after embolization. Variable degrees ofrecanalization and collaterals were observed in 2 days following embolization. Recanalized vessels showed luminalnarrowing with some irregularity in 1-week-and 4-week-groups. Microscopically MFC perse was found in embolizedvessels in both 2-day-and 1-week-groups. Inflammatory reaction was the most severe at 1 week without evidence ofarteritis. Mild inflammatory cell infiltration aroun occluded vessels is noted at 2 days and the inflammatoryreactions subsided at 4 weeks. The author therefore suggests that MFC be regarded effective embolic material inits short term application for clinical use.