Abstract: Objective To explore the expression of Pin X1 in gastric cancer and its impact on the biological behavior of gastric tumor cells. Methods Plasmid transfection was performed to up-regulate the expression of Pin X1,and RNA interference was performed to down-regulate the expression of Pin X1 in gastric cancers. Then western blotting was used to detect the expression of Pin X1 in normal gastric cancer cells,cells with Pin X1- Plasmid transfection and cells with RNAi.CCK8 assay was used to describe cell growth curve of different group cells. Pin X1 expression was also detected by WB in36 pairs of gastric cancer tissues and normal gastric mucosa tissues. The correlation between tumor staging and Pin X1 expression was also calculated. The data was analyzed by SPSS(version 17. 0),and Chi-square test and T test were used to compare the differences between different groups of qualitative or quantitative data. P < 0. 05 was statistically significant. Results The expression of Pin X1 in SGC7901 and MKN28 was lower than in the normal gastric cell line GES-1. After plasmid transfection,Pin X1 was up-regulated in MKN28 cells,which made the growth slower than normal MKN28 cells(P < 0. 05). After RNA interference,Pin X1 was down-regulated in SGC7901 cells,which made the growth faster than normal SGC7901cells(P < 0. 05). The positive rate of Pin X1 expression in gastric cancer tissues was lower than in the adjacent normal mucosa tissues(P < 0. 05),and was related to T staging. Conclusion The expression of Pin X1 in gastric cells and tissues is lower,which may play a negative role of regulation of the malignant behavior of gastric cancer cells.