We report a case of ruptured renal artery aneurysm successfully treated by emergent transcatheter embolization with microcoils. A 66-year-old woman was referred for emergency treatment after presenting with sudden-onset left flank pain and vomiting. Blood examination showed anemia. Computed tomography demonstrated a partly calcified mass with massive retroperitoneal hematoma. With the diagnosis of a ruptured left renal artery aneurysm, emergency angiography was performed. Left renal arteriography demonstrated a saccular aneurysm at the lower aspect of the renal hilum. A total of five microcoils were placed at the arterial branch, including the orifice of the aneurysm. The first coil was partly lodged in a branch near the orifice of the aneurysm that was used as an "anchor" to prevent subsequent coils from migrating and effectively occluding the parent artery with a short segment. Two branches originating from the renal hilum were preserved. The postoperative course was favorable. Endovascular treatments, including coil embolization, appear to be effective, safe, and less invasive than surgery. This method should be considered as a treatment of choice for ruptured renal artery aneurysm.