Abstract: Objective : The E6/E7 oncoproteins play important roles in the initiation and malignant progression of hu-man cervical carcinoma when high-risk types of human papillomaviruses (HPVs) integrate into human chro-mosomes. To evaluate the inhibitory effect and time-efficiency of siRNA, SiHa and CaSki cells positive forHPV16 were transfected with HPV16 E6/E7 siRNAs. Methods : Three specific small interfering RNAs (siRNAs)targeting the E6 or E7 gene were designed and synthesized separately. We investigated the inhibitory effectand time-efficiency of each siRNA and detected the expression levels of mRNA and protein of the targetgenes with RT-PCR and Western blot at 24 hr, 48 hr, 72 hr and 96 hr after transfection with the siRNAs. Re-sults : Each siRNA led to a downregulation of the expression of target genes (P<0.05), but the degree of down-regulation was different. No distinct changes were found in the groups transfected by lipofectemineTM2000without siRNAs. Our experiment indicated that E6-1 siRNA and E7-2 siRNA were the most effective siRNAs.Transfection with either E6-1 or E7-2 siRNA induced a marked decrease of corresponding E6/E7 mRNA andprotein levels in both cell lines (P<0.05), compared with the control group. Expression of untargeted genes didnot change over time. Conclusion : Inhibitory effect varies with siRNAs targeting different sequences of thesame gene. Transfection with either E6 or E7 siRNAs induces a specific and efficient downregulation of thetargeted gene in SiHa and CaSki cells positive for HPV16 (P<0.05) that lasts for 96 hr.