Objective To investigate the clinical value of detection of circulating tumor cells ( CTCs) classified by epithelial cell adhesion molecule ( EpCAM) in peripheral blood of patients with non?small cell lung cancer (NSCLC). Methods Peripheral blood samples (7.5 ml each time) were collected from 47 NSCLC patients. Among them, blood samples were collected at the end of each therapy?cycle in three patients for longitudinal monitoring of CTCs. CTCs were enriched by the depletion of leucocytes using a magnetic bead separation technique, stained with EpCAM, cytokeratin 7/8 and their isotypic control antibodies, respectively, and then identified and counted by multi?parameter flow cytometry. Results In the blood samples from 47 patients, EpCAM?positive CTCs were detected in 64.3%(9/14), 40.0%(4/10) and 43.5%(10/23) of patients in stages Ⅰ?Ⅱ,Ⅲ and Ⅳ, respectively. EpCAM?negative CTCs were detected in 78. 6%( 11/14 ) , 90. 0%( 9/10 ) and 91. 3%( 21/23 ) of patients in stage Ⅰ?Ⅱ, Ⅲ, and Ⅳ, respectively. The total detection rates of EpCAM?positive and EpCAM?negative CTCs were 48.9%(23/47) and 87.2%(41/47), respectively, showing a statistically significant difference between them (P<0.001). According to the stage of the cancer, there was a significant difference between the detection rates of the two types of CTCs in patients of stageⅣ( P=0.001) , but not in stageⅠ?ⅡandⅢ( P>0.05) . The number of EpCAM?negative CTCs was significantly higher than that of EpCAM?positive CTCs in all stages (P<0.05). The frequency of patients with the percentage of EpCAM?negative CTCs >90% was significantly higher in stage Ⅳ patients than that in stage Ⅰ?Ⅱ cases (P=0.030), while the frequency of patients with the percentage of EpCAM?negative CTCs between 50%~90% was significantly lower in the stageⅣthan that in the stage Ⅰ?Ⅱ patients (P=0.001). The treatment of most patients with EpCAM?negative CTCs >50%showed to be ineffective (P=0.033). Conclusion Detection of CTCs classified by EpCAM in peripheral blood is helpful in evaluating the distant metastasis and treatment effectiveness of NSCLC patients.