A 50-year-old man was admitted for evaluation of an abnormal shadow on a chest X-ray. He had experienced pain and swelling in his fingers for three years. He had also noticed that he is impotent. The diagnosis of Klinefelter syndrome and rheumatoid arthritis (RA) was established by clinical findings and chromosomal analysis. Transbronchial biopsy revealed adenocarcinoma and right upper lobectomy was performed. Open lung biopsy showed interstitial pneumonia. In conclusion, we reported a rare case of lung cancer, rheumatoid arthritis and RA lung associated with Klinefelter syndrome.