Objective: To investigate the effects of nuclear factor 5 of activated T cells (NFAT5) on proliferation and apoptosis of human gastric cancer MGC803 cells and to explore the possible mechanisms. Methods: Three siRNAs targeting NFAT5 gene (siRNA2567, siRNA2714 and siRNA4562) and one negative control siRNA were designed and chemically synthesized before transfected into human gastric cancer cell line MGC803 by liposome. Real-time PCR was used to detect the changes of N F AT 5 mRNA expression in MGC803 cells to further pick out the siRNA that most effectively inhibit the expression of N F AT 5 . Further, Real-time PCR and Western blotting assay were carried out to test mRNAand protein levels of NFAT5 and S100A4 in cells 48 h after N F AT 5 -siRNAtransfection. Then, CCK-8 assay and FCM assay were used to detect the influence of silencing N F AT 5 on cell proliferation and apoptosis, respectively. Results: siRNA2567 was the most effective siRNA that significantly inhibited the expression of N F AT 5 mRNA ( P <0.01), and thus was validated as NFAT5-siRNA. Real-time PCR and Western blotting assay confirmed that both mRNA and protein levels of NFAT5 and S100A4 were down-regulated in cells 48 h after N F AT 5 -siRNAtransfection. Compared with NC-siRNAgroup, the proliferation ability of MGC803 cells in the N F AT 5 siRNAgroup was significantly down-regulated at 72 h and 96 h ( P <0.01).And FCM assay showed that compared with NC-siRNA group, cell apoptosis rate of N F AT 5 -siRNA group was significantly increased from (2.7±0.2)% to (7.9±0.2)%, ( P <0.01) 48 h after N F AT 5 -siRNA transfection. Conclusion: N F AT 5 -siRNA transfection can silence N F AT 5 gene expression in gastric cancer MGC803 cells effectively. N F AT 5 may inhibit proliferation and promote cell apoptosis of gastric cancer cells possibly through regulating S100A4 expression.