Microscopic polyangiitis (MPA) is an anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis characterized by inflammation of small-sized vessels. Although there have been some reports of ANCA-associated vasculitis presenting as aortitis syndrome, MPA rarely involves large-sized vessels such as the aorta. We report an unusual case of MPA combined with severe acute aortic valve insufficiency in a 56-year-old man. He initially presented with prolonged fever, skin rash, and rapidly progressive glomerulonephritis. P-ANCA and anti-myeloperoxidase (MPO) antibodies were positive, but the c-ANCA and anti-proteinase-3 antibodies were negative. Skin biopsy of the lower leg showed necrotizing arteritis. Kidney biopsy was also performed, which revealed diffuse necrotizing and crescentic glomerulonephritis (GN) consistent with pauci-immune ANCA-associated GN. Serial echocardiographic evaluations revealed aortic valve changes and worsening acute aortic valve insufficiency over a two-month period. Despite intensive treatment, our patient developed sudden cardiac arrest and died. Our patient demonstrated typical clinical features and histopathologic findings for systemic vasculitis and had a positive anti-MPO antibody, all of which were consistent with the diagnosis of MPA. Thus, MPA may have been the cause of acute aortic valve insufficiency in this case.