Abstract: Objective: To detect the expression of CEA mRNA in patients with non-small cell lung cancer (NSCLC) and to in-vestigate its significance. Methods: The blood samples were taken from peripheral veins of 70 patients with NSCLC and 18 patients with benign diseases at 3 intervals during the surgery. The transcription of carcinoembryonic antigen messen-ger ribonucleic acid(CEAmRNA) was assayed by nested reverse transcriptase polymerase chain reaction(RT-PCR) and micro-fluid chip. Results: The CEAmRNA positive rates at each of the 3 time spots are as follows: 50% in the samples col-lected at the beginning of the surgery(group 1), 62.8% in the samples collected when ligating the pulmonary vein(group 2) and 57.1% in samples collected 1 hour after pulmonary vein ligation (group 3). A significant difference was found between group 1 and group 2 (χ² =7.114, P<0.05). Conclusion: Cancer cell dissemination during surgery was demonstrated indirect-ly in our study. When to ligate the pulmonary vein (earlier or later) may affect the quantity of tumor cells spread into the circulation.