Lung cancer is the most common cause of cancer-related deaths in men and women all over the world. Although themost common cause of lung cancer is long-term exposure to tobacco smoke, the role of genetic factor for the cell defense mechanism against lung cancer, such as MnSOD, should also be considered. MnSOD is the major antioxidant in matrix mitochondria, which plays a pivotal role in eliminating anion superoxide free radical generated from the tobacco smoke. The genotype of human MnSOD which is related to various cancers has been reported, but the correlation between the genotype and the enzyme activity remains unknown. The aim of this study is to analyze the expression (mRNA and enzyme specific activity) and genotype of MnSOD in lung cancer cells of smoker patients. Samples were normal and lung cancer cells of patients operated in Persahabatan Hospital from May to December 2008 (3 patients), as well as lung cancer cells extracted from FFPE collection of Persahabatan Hospital. Leukocyte cells of 15 healthy subjects aged more than 40 years with a history as a smoker for more than 10 years were used as controls. MnSOD gene expression was analyzed based on relative mRNA level and specific activity of MnSOD in lung cancer and leukocyte cells. The genotyping was performed using PCR-RFLP. The result showed that the lung cancer cells observed in this study have a Val/Val genotype frequency of 100%, thus Ala/Val genotype could not be found compared to the leukocyte cells of smoker controls (13.3%). The MnSOD specific activity in lung cancer of smoker patients is higher than in leukocyte cells of smoker controls. Result of MnSOD gene expression at the level of mRNA and protein activity was contradictory. Compared to the expression of MnSOD in the normal lung cells of patients, in the lung cancer cells the level of MnSOD mRNA was lower (0.382 times), whereas its specific activity was higher (1.988 times). Therefore, in this study we could conclude the role of MnSOD as tumor suppressor in lung cancer. The enhancement of MnSOD specific activity in lung cancer cells might be one of the cell responses against the exaggerated attack of ROS particularly in smokers. Further studies are required to analyze the correlation between MnSOD genotype and response or prognosis of cancer therapy.