Multiple primary lung cancer is a rare disease entity and its clinical characteristics, treatment, and prognosis are poorly described. But the multiple primary lung cancer have a more favorable prognosis than locally recurrent or metastastic disease. Therefore, appropriate identification of multiple primary lung cancer will be very important. We have experienced a case of stage I multiple primary lung cancer in a 76-year-old male with two large mass in the right lower lobe without metastasis in the mediastinal lymph nodes with right mid and lower lobectomy. The microscopic pictures revealed adenocarcinoma in the one & small cell carcinoma in another. The post-operative courses were in uneventful for 4 months & but he was treated with chemotherapies, 2 times for complete remission of small cell carcinoma to now after discharge.