Microfibrillar Collagen (MFC) a effective topical hemostatic agent may be a highly effective embolic material which gas availability ease of use through catheter and potent thrombogenicity and causes occlusion at the level of the arterioles leading to extensive tissue infarction but is not widely used due to early recanalization of the vessels embolized and to known granulomatous arteritis. The author designed an animal experiment on transarterial embolization using MFC for the patients with hemorrhage malignant lesion etc in which preoperative vascular occlusion is desirable. Transcatheter embolization with MFC suspension was performed in right renal arteries of 22 rabbits. Post-embolization angiography gross morphologic and microscopic ex-aminations of the kidneys embolized were evaluated 2 days 1 week and 4 weeks after embolization . Variable degrees of recanalization and collaterals were observed in 2 days 1 week and 4 weeks-groups. Microscopically MFC perse was found in embolized vessels in both 2-day-and 1-week-groups. Inflammatory reaction was the most severe at 1 week without evidence of arteritis. Mild inflammatory cell infiltration around occluded vessels is noted at 2 days and the inflammatory reactions subsided at 4 weeks. The author therefore suggests that MFC be regarded effective embolic material in its short term application for clinical use.