A thirty-two-year-old male patient was admitted to our hospital for persistent fever, cough, and pleuritic pain. Chest X-ray image showed infiltration in the middle lobe of the right lung, and he was diagnosed with pulmonary actinomycosis by transbronchial lung biopsy. The symptoms improved after a 12-month antimicrobial treatment; however, his symptoms and chest X-ray image worsened 3 months after cessation of antibiotics. We again treated the patient successfully with antibiotics for 15 months, but his condition was subsequently aggravated 2 months later. He refused our recommendation to operate. Therefore we continued antimicrobial treatment for an additional 20 months. Currently there has been no recurrence for 2 years. Antibiotics for 6 to 12 months to treat pulmonary actinomycosis are recommended; however, we experienced a case that demonstrated repeated exacerbation after the standard treatment period.