Gefitinib is a molecular targeting agent and more effective in patients with characteristics of oriental ethnicity, female gender, adenocarcinoma and non-smokers. It is sometimes effective in smokers, but few papers have focused on the association between efficacy and smoking history. The aim of this study is to evaluate the association between efficacy of gefitinib and patients' characteristics, especially smoking history. Between July 2002 and September 2006, 89 patients were diagnosed as non-small cell lung cancer and administered gefitinib. Eighty of them were assessable for efficacy and toxicity of gefitinib. Response rate was 16.2% and 39.6%(p=0.031)in smokers and non-smokers. Survival was statistically greater in non-smokers. In smokers, there are more cases which showed response to gefitinib with a lower smoking index and longer duration after smoking cessation. Smoking index and duration after smoking cessation should be considered when gefitinib is administered or EGFR mutation analysis is conducted in patients with non-small cell lung cancer.