We present the case of a 55-year-old man with ruptured arterial aneurysm accompanied by microscopic polyangiitis in the kidney. He was admitted to our hospital because of general fatigue, fever and serious numbness of his extremities. Microscopic polyangiitis (MPA) was diagnosed on the basis of cardinal symptoms, including rapidly progressive glomerular nephritis, peripheral nerve disorder and the lung abnormality, as well as positive MPO-ANCA findings. Hemodialysis had to be started on admission because of renal failure. Renal biopsy demonstrated necrotizing glomeruli, crescent formation with interstitial infiltrates. There were no immune deposits on immunofluorescence study or electron micrographs. The pathological diagnosis was necrotizing glomerulonephritis involving small and medium-sized arteries. He was treated with intravenous semi-pulse methylprednisolone therapy because of the intensely pathological renal activation and the abnormal shadow on chest X-ray. The inflammatory reaction subsequently improved, MPO-ANCA decreased and the lung lesions diminished. He complained of sharp pain of sudden onset on his left side. His hemoglobin dropped from 9.8 g/dl to 6.0 g/dl developed in the subsequent hours, but there were no sign of hemorrhage. Abdominal CT scan showed a large left-sided perinephric, intracapsular hematoma. Selective arterial angiography showed multiple aneurysms in renal and hepatic arteries. No active bleeding was present and he recovered with transfusion, supportive therapy and monitoring alone. Multiple aneurysms detected by angiography in the renal and hepatic arteries showed improvement. He is currently stable on regular hemodialysis treatment with a low dose of oral prednisolone.