Pulmonary actinomycosis in healthy subjects is a rare entity, and its spontaneous remission is very rare. Here we report a case of pulmonary actinomycosis in a healthy subject who was diagnosed by transbronchial lung biopsy and showed spontaneous remission without treatment. A 57-year-old Japanese man with no medical history visited our hospital because of a nonproductive cough of several weeks. His chest X-ray film and computed tomography showed mass-like consolidation with a cavitation in the left upper lobe and mediastinal lymphadenopathy. Laboratory data showed a slight elevation of C-reactive protein. Transbronchial lung biopsy specimens taken from the left B¹⁺² showed actinomycosis in pulmonary parenchyma. His clinical symptoms, chest X-ray, and computed tomography findings, spontaneously improved with no medication within a half-year, and no exacerbation has been observed for more than 5 years. Spontaneous remission of pulmonary actinomycosis in a healthy subject is very rare. Pulmonary actinomycosis is a rare entity; however, clinicians should be aware of this disease in cases with pulmonary nodules and mass opacities.