Objective:To investigate the expression of targeted gene CK19 mRNA in peripheral blood of the patients with gastric cancer and its correlation with biological behaviors of gastric cancer. Methods: CK19 mRNA in peripheral blood of 56 patients with gastric cancer was detected by RT-PCR method. Meanwhile, the peripheral blood of 12 healthy volunteers and 12 gastric cancer tissues were respectively selected as negative and positive controls. The correlation between CK19 mRNA expression in peripheral blood of the patients with gastric cancer and clinical pathological characteristics was analyzed. Results: The positive rate of CK19 mRNA in peripheral blood of 56 patients with gastric cancer was 58.9% (33/56). The expression rate of CK19 mRNA in 12 gastric cancer tissues came up to 100.0% (12/12), whereas CK19 mRNA in peripheral blood of 12 healthy volunteers was expressed negatively. CK19 mRNA expression was signiifcantly related to the clinical staging of gastric cancer and lymphatic metastasis (P<0.05), but had no association with gender, age, cell differentiation and inifltration depth (P>0.05). Conclusion: The application of RT-PCR was highly sensitive and speciifc in detecting the CK19 mRNA in peripheral blood of patients with gastric cancer, in which CK19 mRNA is expected to be a tumor marker for judging the metastasis and recurrence and evaluating the efifcacyof gastric cancer.