Pleural fluid rarely occurs in patients with progressive systemic sclerosis (PSS) or polymyositis (PM) with no lesions in the pulmonary area. Pleural fluids in patients with autoimmune diseases are mostly dominated by monocytes and lymphocytes but very rarely contain increased eosinophils. We report a 55-year-old male with PSS-PM overlap syndrome and eosinophilic pleural effusion. Air invasion into the pleural cavity and the antituberculous therapy could be ruled out as causes for the patient's eosinophilic pleural effusion, because the differential eosinophil count was already as high as 19% from the first thoracentesis before the start of antituberculous therapy. Infections and malignant tumor also were unlikely causes based upon the negative pleural fluid results and the negative pleural biopsy findings, except for nonspecific inflammation. After the administration of corticosteroid, the pleural effusion decreased promptly, with normalization of serum creatine phosphokinase and C-reactive protein concentrations.