Objective: To investigate the CDH17 expression in gastric cancer cells and its influence on the invasiveness of gastric cancer cells. Methods: The invasion ability and expressions of CDH17, epithelial marker E-cadherin and mesenchymal marker N-cadherin in normal gastric mucosal GES-1 cells, and gastric cancer MGC803 and BGC823 cells were examined by Transwell migration assay, immunofluorescence staining and Western blot analysis, respectively, and the changes in above parameters in the two types of gastric cancer cells after transfection with CDH17siRNA were also determined. Results: No invading cells or CDH17 and N-cadherin expression, but evident E-cadherin expression was seen in normal gastric mucosal GES-1 cells. In either MGC803 or BGC823 cells compared with GES-1 cells, there was considerable number of invading cells as well as marked CDH17 and N-cadherin expressions, but significantly reduced E-cadherin expression (all P<0.05), and further, the changes in these parameters in highly invasive MGC803 cells were more evident than those in less invasive BGC823 cells. After CDH17siRNA transfection, the changes in above parameters in both types of gastric cells were significantly weakened compared with those before transfection, and the differences of which between the two types of cells were decreased (all P>0.05). Conclusion: High CDH17 expression can promote invasion ability of gastric cancer cells, probably via epithelial-mesenchymal transition.