Objective To investigate the effect of enhancer of zeste homolog 2 (EZH2) knockdown on chemosensitivity to oxaliplatin in human gastric cancer cell line SGC7901.Methods Small interfering RNA (siRNA) fragments were designed and synthesized for EZH2 mRNA sequence and divided into siRNA-1 group,siRNA-2 group and siRNA-3 group.They were transfected into gastric cancer cell line SGC7901.The negative control group and blank control group were set up at the same time.The expressions of EZH2 mRNA and protein in the SGC7901 cells were detected by quantitative real-time polyme-rase chain reaction (qRT-PCR) and Western blotting.CCK-8 assay was used to detect cell proliferation inhibition rates of SGC7901 cells treated by different concentrations of oxaliplatin.Results After transfection of EZH2 siRNA,the relative expression levels of EZH2 mRNA in siRNA-1 group,siRNA-2 group,siRNA-3 group were 0.615 ±0.190,0.241 ±0.152 and 0.450 ± 0.097.The relative expression levels of EZH2 mRNA of the three groups were lower than that in the negative control group (1.165 ± 0.376),and the differences were statistically significant (P =0.028;P =0.002;P =0.007).After transfection of the best siRNA fragment into SGC7901 gastric cancer cells,the relative expre-ssion levels of EZH2 protein in interference group,blank control group and negative control group were 0.036 ± 0.017,0.362 ± 0.026 and 0.398 ± 0.036,and the diffe-rence among the three groups was statistically significant (F =157.745,P ＜ 0.001).The difference between interference group and negative control group was statistically significant (P =0.001),as compared with the blank control group (P =0.002).When oxaliplatin concentration was 2,4,8 and 16 μg/ml,the differences of cell proliferation inhibition rate among interference group,negative control group and blank control group were statistically significant [(18.107 ± 2.822)％,(5.867±2.272)％,(5.333 ±1.883)％,F=28.185,P=0.001;(54.953 ±2.550)％,(22.177±1.871)％,(20.077±6.032)％,F=74.206,P＜0.001;(60.337±1.641)％,(34.597± 3.592)％,(30.227 ±5.273)％,F=54.897,P＜0.001;(78.340 ±2.081)％,(61.857 ±3.507)％,(63.077 ± 8.473) ％,F =8.586,P =0.017].There was no significant difference among groups of oxaliplatin at the concentration of 32 μg/ml [(83.450 ±3.715)％,(72.190 ±3.948)％,(70.731 ± 17.080)％,F=1.358,P =0.326].The median inhibitory concentration (IC50) of oxaliplatin in siRNA group,negative control group and blank control group were 5.178,12.643,13.601 μg/ml.Conclusion Down-regulation of EZH2 gene expression can significantly inhibit the proliferation of gastric cancer cells,and effectively enhance the sensitivity of gastric cancer cells to oxaliplatin,which indicates EZH2 may play important roles in the development of gastric cancer chemotherapy.These results provide an important theoretical basis for gene therapy of gastric cancer.