Pulmonary actinomycosis (PA) is a rare subacute or chronic infectious disease. As simple culture of Actinomyces in BAL, as with sputum, may represent colonization, the diagnosis of PA relies on pathological examination. The preferred treatment is long-term, high-dose penicillin. A 6–12-month-course of antibacterial treatment is the rule in extended PA, although the optimal duration of treatment has not been investigated through randomized trial. In this article, we report a case presented with slowly-progressing pulmonary cavitary lesions. Actinomyces odontolyticus was detected in sputum specimen harvested by tracheoscopy. The clinical diagnosis was PA, which gradually improved with prolonged treatment of penicillin and ornidazole. This is followed by a discussion of diagnosis and treatment, especially in terms of treatment.