Microscopic polyangiitis (MPA) is a systemic necrotizing vasculitis affecting small vessels without necrotizing granulomatous inflammation and is commonly associated with necrotizing glomerulonephritis. Diagnosis is based on typical clinical features, the presence of antimyeloperoxidase-antineutrophil cytoplasmic antibodies (MPO-ANCA), and histopathologic findings. Cases of pathologically proven small-vessel vasculitis in nasal biopsy specimens are sparse. Here we report a patient with MPA that was histopathologically confirmed by nasal and paranasal biopsy. A 67-year-old man presented with fever and general fatigue. Laboratory examinations showed severe inflammation and acute progressive renal failure. The serum MPO-ANCA level was elevated. The patient also had nasal polyps that seemed to be nonspecific chronic sinusitis. To obtain a pathologic diagnosis, bilateral ethmoidectomy and nasal polypectomy were performed. Pathological findings revealed vasculitis of small vessels in the mucosal surface. MPA was diagnosed on the basis of clinical symptoms, elevated MPO-ANCA and the pathological findings of the nasal and paranasal surgical specimen.