Background: Circulating tumor cells (CTCs) have potential utility in various clinical application for cancer management. In this study, we evaluated whether circulating tumor cells (CTCs) provide early diagnostic information and/or precisely indication of patient response to chemotherapy. Methods: 56 patients with newly diagnosed lung cancer, 42 patients with nonmalignant pulmonary disease and 27 healthy controls were enrolled in this study. CTCs were measured at baseline in all eligible subjects and after two cycles of chemotherapy in 25 advanced lung cancer patients, with a strategy of negative enrichment combined with immunostaining-fluorescence in situ hybridization (imFISH). The receiver operating characteristic (ROC) curve was plotted to determine the sensitivity and specificity of the CTC detection for diagnosis. Kaplan-Meier curve and two-sided log-rank test were used for univariate survival analyses. Results: The number of CTCs was significantly increased in lung cancer patients, compared with benign lung disease patients and healthy controls. And it reached 87.5% sensitivity and 95.7% specificity at a cutoff value of 2 cells/3.2ml (AUC = 0.975, 95%CI, 0.953-0.998, p＜0.001).Moreover, the sensitivity of CTCs was much higher than individual or the combination of serum tumor markers, especially in the early detection of lung cancer. Twenty-five advanced lung cancer patients were subsequently followed for an average of 18.2 months (range 6-36 months) ， during which all patients experienced disease progression, and 16 patients died. A change in CTC count after two cycles of chemotherapy was highly predictive for PFS (13.5 v 8.5 months; p = 0.025) and OS (27.6 v 16.8 months; p = 0.009) in favor of a reduction in CTC number compared with an increase. Interestingly, among the patients whose post-treatment computed tomography(CT) results indicated stable disease(SD), PFS (14.0 v 8.7months; p = 0.033) and OS(25.8 v 15.9 months; p = 0.018) in patients whose CTC number decreased after two cycles of treatment were still significantly longer than those whose post-treatment CTCs number increased or unchanged. Conclusions: CTCs may act as precise biomarker for early detection and therapy monitoring that could compensate for imaging.