Background. Bronchopulmonary actinomycosis is a chronic granulomatous inflammatory disease that is difficult to diagnose by bronchoscopy. The appropriate duration of treatment of actinomycosis has been widely debated. Case 1. A 59-year-old woman was referred to our institution with atelectasis in the right lower lobe. Bronchoscopy revealed that the orifice of the right lower bronchus was obstructed by an inflamed polyp. A biopsy of the polyp from the peripheral side of the bronchus confirmed the diagnosis bronchopulmonary actinomycosis. The polyp disappeared after seven months of antibiotic therapy. Case 2. A 53-year-old woman was referred to our institution with a fever and hypoxemia. Bronchoscopy revealed that the left B5 bronchus was obstructed by an inflamed polyp. Bronchial lavage after a tissue biopsy revealed Gram-positive filamentous bacilli, suggesting bronchopulmonary actinomycosis. The polyp regressed after seven months of antibiotic treatment. Conclusion. A biopsy from the peripheral side of a bronchial polyp using endobronchial ultrasonography with a guide sheath is useful for the diagnosis of actinomycosis with an inflamed polyp. The reduction in size of an inflamed polyp caused by actinomycosis can assist in the evaluation of the efficacy of antibiotics.