Diffuse alveolar hemorrhage is a rare but serious and frequently life-threatening complication of a variety of conditions. The first goal in the management of patients with diffuse alveolar hemorrhage is to achieve or preserve stability of the respiratory status. Subsequently, the differential diagnosis is aimed at the identification of a remediable cause of the alveolar hemorrhage. The most common causes of diffuse alveolar hemorrhage with glomerulonephritis are microscopic polyangiitis and Wegener's granulomatosis, followed by Goodpasture syndrome and systemic lupus erythematosus. Microscopic polyangiitis (MPA) is a distinct systemic small vessle vasculitis affecting small sized vessels with few or no immune deposits and with no granulomatosus inflammation. The disease may involve multiple organs such as kidney, lung, skin, joint, muscle, gastrointestinal tract, eye, and nervous system. MPA is strongly associated with antineutrophil cytoplasmic autoantibody (ANCA) that is a useful serological diagnostic marker for the most common form of necrotizing vasculitis. Our report concerns a case of microscopic polyangiitis with diffuse alveolar hemorrhage in a 54-year-old man. He was admitted to our hospital due to dyspnea upon exertion and recurrent hemoptysis. Laboratory findings showed hematuria, proteinuria and deterioration of renal function. In the chest CT scan, diffuse ground glass appearance was seen in both lower lungs. A lung biopsy revealed small vessel vasculitis with intraalveolar hemorrhage and showed a positive reaction to against perinuclear ANCA. The patient was treated with prednisolone and cyclophosphamide. Chest infiltration decreased and hemoptysis and hypoxia improved. He is still being followed up in our hospital with a low dose of prednisolone.