To investigate the RNA interference (RNAi) effect induced by vector-derived small in-terfering RNA (siRNA) targeting the three gatekeeper genes (Rad52, Ku70, Ku80) and screen the more effective target sites from candidates for further research, by using siRNA design tools online, we selected 2 candidate sequences directed to every gatekeeper gene. According to the sequences, six vector-derived siRNAs (denoted psiRNA1-6) and one mocking psiRNA7 were constructed. Among them, psiRNA1 and psiRNA2 targeted Rad52, psiRNA3 and psiRNA4 to Ku70, psiRNA5 and psiRNA6 to Ku80. The mocking psiRNA7 was used as control. After sequence identification, the seven plasmids were transfected into HepG2 cell line. siRNA-induced silencing of gatekeeper genes was determined by using RT-PCR at RNA level and Western Blot at protein level. The results showed that the six plasmids specifically targeting the coding region of gatekeeper genes were successfully designed and constructed. To some extent, the six plasmids could reduce the expression of target gene. Comparatively, the plasmid-derived siRNA psiRNA1, psiRNA4 and psiRNA5 were more effective than their counterparts. The results suggest that the gene silencing efficiency of siRNA is different, depending on their targeted region, and siRNA may provide us with practical tools for further study on the three gatekeeper genes, i.e. Rad52, Ku70, Ku80. To investigate the RNA interference (RNAi) effect induced by vector-derived small in-terfering RNA (siRNA) targeting the three gatekeeper genes (Rad52, Ku70, Ku80) and screen the more effective target sites from candidates for further research, by using siRNA design them online, we selected 2 candidate sequences directed to every gatekeeper gene. According to the sequences, six vector-derived siRNAs (expressed psiRNA1-6) and one mocking psiRNA7 were constructed. Among them, psiRNA1 and psiRNA2 targeted Rad52, psiRNA3 and psiRNA4 to mK70, psiRNA5 and psiRNA6 to Ku80. The mocking psiRNA7 was used as control. After sequence identification, the seven plasmids were transfected into HepG2 cell line. siRNA-induced silencing of gatekeeper genes was determined by using RT-PCR at RNA level and Western Blot at protein level. The results showed that the six plasmids specifically targeting the coding region of gatekeeper genes were successfully designed and constructed. To some extent, the six plasm The lytic ids could reduce the expression of the target gene. Comparatively, the plasmid-derived siRNA psiRNA1, psiRNA4 and psiRNA5 were more effective than their counterparts. The results suggest that the gene silencing efficiency of siRNA is different, depending on their targeted region, and siRNA may provide us with practical tools for further study on the three gatekeeper genes, ie Rad52, Ku70, Ku80.