Abstract: Objective To screen for effective siRNAs for STAT5A gene and study the effect of suppression of STAT5A gene expression on proliferation and apoptosis of human hepatocellular carcinoma cell line HepG2, and to explore the role of STAT5A in generation and development of hepatocellular carcinoma. Methods Three siRNAs targeted at STAT5A gene were designed and synthesized chemically, and then transfected into HepG2 cells with liposome transfection method. The expression levels of STAT5A mRNA and protein were detected by semi-quantitative reverse transcript polymerase chain reaction (RT-PCR) and immunoblotting assay (Western blot) respectively, and then the effective sequence was selected based on the interference effi ciency. MTT method was used to detect the cell proliferation, and FCM was used to detect the cell apoptosis after the optimal siRNA was transfected. Results The three siRNAs could inhibit STAT5A gene expression at both mRNA and protein levels in various degrees, and siRNA-3697 was the most effi cient, with the inhibition rates of STAT5A mRNA and protein expressions of 72.03％ and 66.27％（P<0.05），respectively. The result of MTT analysis showed that the cell growth rat of the experiment group was decreased and the proliferation inhibition rate was inhibited signifi cantly after 1-4d of transfection(P<0.05). And FCM assay indicated that the apoptotic rate of the experiment group was 37.33% after 48h of transfection （P<0.05). Conclusion An effectual siRNA for STAT5A gene was successfully screened out, and this siRNA could inhibit the expression of STAT5A gene efficiently,causing inhibition of the proliferation of HepG2 cells, and promotion of apoptosis obviously.