Abstract： Objective To investigate independent prognostic factors for overall survival (OS) in extensive disease small cell lung cancer (EDSCLC). Methods Between January 2003 and December 2006, 154 patients diagnosed with extensive stage small cell lung cancer were enrolled in this study.Prognostic factors such as gender, age, performance status, smoking history, weight loss, distant metastasis, the number of matastasis, brain metastasis, the cycle of chemotherapy and thoracic radiation therapy (TRT) for EDSCLC patients were evaluated by univariate and multivariate analysis. Results The median following-up time was 40. 5 months. The rate of follow-up was 92. 2%. The MST and overall survival rates at 3-year in smoking group and no-smoking group were 13 months, 11.8% and 17 months,22. 8%,respectively (χ2=3.40,P =0. 064);in ChT/TRT group and ChT group, they were 17. 2 months, 17.9%and 9.3 months,13.9%, respectively(χ2=10.47,P=0.001);and in the cycle of chemotherapy ≥4 group and ＜ 4 group, they were 16 months, 20. 1% and 9.3 months, 2. 9%, respectively (χ2=17.79,P=0. 000). By multivariate analysis, smoking history was a statistically significant unfavorable factor for OS in EDSCLC patients (versus no-smoking, hazard ratio (HR)=1.462, χ2=4.40, P=0.036). In addition, ≥4 cycles of chemotherapy and TRT were favorable prognostic factors ( ≥4 cycles vs ＜4 cycles, HR =0. 420,χ2 = 17. 17, P = 0. 000; ChT/TRT vs ChT, HR = 0. 634, χ2 = 6. 20, P = 0. 013). Conclusions Smoking is a independent unfavorable prognostic factor and ≥ 4 cycles of chemotherapy And TRT are independent favorable prognostic factors for OS in EDSCLC.