Caplan originally described distinctive pulmonary nodules in miners who had suffered from rheumatoid arthritis. Later, the pulmonary nodules, together with a history of rheumatoid arthritis and exposure to inorganic dust were called Caplan's syndrome. This syndrome has been described by case reports in many countries but only two cases have been reported in Korea up to now. The patient in this case report was a 70-years-old man who had worked in the construction field for 20 years mainly de-molishing buildings. He was diagnosed with silicosis by a lung biopsy 1 year prior to admission. He suddenly developed arthralgia and morning stiffness in multiple joints 2 weeks prior to admission. Chest imaging revealed ag-gravation of the bilateral pulmonary nodules. He was diagnosed with seropositive rheumatoid arthritis. The lung nodules, arthralgia, and morning stiffness improved clinically after treatment with the corticosteroid and disease modifying antirheumatic drugs.