Actinomycosis is an indolent infectious disease characterized by pyogenic response and necrosis, followed by intense fibrosis. The main forms of human actinomycosis are cervicofacial, pulmonary, and abdominopelvic type. Pulmonary actinomycosis accounts for 15% to 20% of total cases and unfortunately, clinical manifestations and radiologic findings are nonspecific. Small pleural effusion or empyema may develop in advanced disease but massive empyema is infrequent and rarely reported. We report a case of huge empyema caused by pulmonary actinomycosis in a 55 year-old man, presented with one-month history of productive cough and fever. The CT scan revealed a huge cavity with air-fluid level occupying the left hemithorax. Empyema caused by actinomycosis was confirmed microscopically by demonstration of sulfur granules in empyema sac through thracotomy. Decortication and surgical resection of empyema sac and destructed lung was accomplished and followed by intravenous infusion of penicillin G.