Two cases of renal artery embolism treated by selective intra-arterial infusion of tissue plasminogen activator (t-PA) are reported. A 74-year-old woman with atrial fibrillation presented with left flank pain of 54-hour duration. Selective renal angiography revealed embolic obstruction of multiple segmental arteries in the left kidney. She was treated by one-shot intra-arterial t-PA infusion (8,000,000 units) and intravenous heparinization (25,000 units/3 days). Although fibrinolysis was successful except for most distal arterial branches, complete recovery of renal function was not obtained. A 66-year-old man presented with complete obstruction of left main renal artery. He had hyperthyroidism and atrial fibrillation. At 75 hours after onset of left flank pain, he was treated by one-shot intra-arterial t-PA infusion (18,000,000 units) and intravenous heparinization (4,000 units/24 hours). His renal function was recovered completely. Selective intraarterial t-PA infusion is considered an effective treatment for renal artery embolism.