Microscopic polyangiitis is a necrotizing vasculitis, characterized by inflammation of small vessels (capillaries, venules, and arterioles) with few or no immune deposits. The kidneys are the most commonly affected organs and are involved in 90% of patients, whereas pulmonary involvement occurs in a minority of cases (10% to 30%). In cases of lung disease, diffuse alveolar hemorrhage with pulmonary capillaritis is the most common manifestation. Microscopic polyangiitis is strongly associated with antineutrophil cytoplasmic autoantibody, which is a useful diagnostic serological marker. We report a case of microscopic polyangiitis presented as pleural effusion in a 67-year-old female. Pleural effusions have been reported in some cases previously, but the number of cases were small and their characteristics have not been well described. This report describes characteristic findings of pleural fluid and its histological features in a case of microscopic polyangiitis.