Eosinophilic pleural effusion (EPE) is defined as a pleural effusion that contains at least 10% eosinophils. EPE occurs due to a variety of causes such as blood or air in the pleural space, infection, malignancy, or an autoimmune disease. Undifferentiated connective tissue disease (UCTD) associated with eosinophilic pleural effusion is a rare condition generally characterized by the presence of the signs and symptoms but not fulfilling the existing classification criteria. We report a case involving a 67-year-old man with UCTD and EPE, who has been successfully treated with a single intrapleural corticosteroid injection.