Background Progress in gastric cancer is hampered by the lack of diagnostic markers useful for clinical practice.This study aims to establish a quantitative method for human carcino-embryonic antigen(CEA)mRNA by real-time RT-PCR.Its application was further evaluated by detecting circulating tumor cells in the peripheral blood of gastric cancer patients.Method and Results The concentration of each component in the detection kit was optimized; the stability,sensitivity,and specificity were determined.The expression level of CEA mRNA was detected in the samples of peripheral blood.Optimized primers and probes were obtained,and setting standards were successfully prepared.Through establishing the positive and negative control materials,the specificity,sensitivity,accuracy and quality control were determined for the detection kit.The specificity and accuracy were both more than 95%,and the sensitivity was of 100 copies/ml(whole peripheral blood).The detection results of CEA mRNA in peripheral blood samples showed that all the samples were positive for 15 gastric cancer patients clinically diagnosed with metastasis; and 12 samples were positive and other 13 samples were negative among 25 gastric cancer patients without clinically diagnosed with metastasis or not; all the samples were negative for 10 gastric ulcer patients; and all the samples were negative for 10 healthy control.Conclusion The quantitative RT-PCR assay for CEA mRNA could be used for the detection of circulating tumor cells in peripheral blood of gastric cancer patients,which would be valuable for the diagnosis and clinical-decision making for gastric cancer patients.