Abstract: Objective: To investigate the CK19 mRNA expression in peripheral blood and its significance in patients with non-small cell lung cancer. Methods: Reverse transcriptase polymerase chain reaction (RT-PCR) was used to amplify the CK19 mRNA in blood samples from 43 patients with NSCLC, and controls including 20 patients with benign lung diseases and 20 healthy volunteers. Results: The positive rate of CK19 mRNA in peripheral blood was 56% in patients with lung cancer and 5% in the controls, showing a significant difference between patients with NSCLC and controls (P<0.01). The positive rate had significant correlation with the TNM staging and lymph node metastasis but histopathologic types. Conclusions: RT-PCR amplification of CK19 mRNA is a sensitive method to detect the early circulating cancer cell for patients with lung cancer. It may help doctors to evaluate the cancer more correctly and make the best treatment plan. Further studies with more samples and long-term follow-up are needed.