An extremely rare disease with a slow course, actinomycosis has a high mortality risk when not properly treated. Pulmonary actinomycosis is clinically and radiologically analogous with tuberculosis, foreign body aspiration, lung abscess, or lung cancer. Therefore, it often causes misdiagnosis or delay in diagnosis. A 65-year-old male patient, being followed up with the diagnosis of chronic obstructive pulmonary disease (COPD) and lung adenocarcinoma, was admitted to our outpatient clinic with complaints of chronic cough. On chest CT, a cavitary lesion in the upper lobe of the right lung was observed. Sputum Acid Fast Bacilli (AFB) was negative for 3 consecutive times, fungal direct examination was negative, and there was no growth in mycobacterium culture and fungal culture. Flexible bronchoscopy revealed a raised, hard, white-colored lesion on the mucosa obliterating the apical and anterior segment bronchial entrance of the right lung upper lobe. A diagnosis of actinomycosis was made with sulfur granules seen in the pathology as a result of biopsy and lavage. Detection of sulfur granules in biopsy is essential for the diagnosis of actinomycosis, and a nearly complete response is usually obtained with long-term antibiotic treatment. Alternative methods such as surgical debridement should be considered in cases that do not respond to antibiotic treatment.