To study the inhibitory effects of plasmid-derived small interfering RNA(siRNA)andsynthetic siRNA on the expression of the hepatitis B virus surface(HBs)gene,three plasmid-derived siRNAsand one synthetic siRNA that complement the coding region of the HBs gene were prepared.The HBsexpression plasmid pHBs-EGFP was also constructed.HeLa cells were co-transfected with pHBs-EGFPand the above siRNAs.The HBs mRNA quantities were measured by reverse-transcription PCR,and thelevel of HBs-EGFP fusion protein was quantified by fluorescent microscope.The concentrations of thehepatitis B virus surface antigen(HBsAg)derived from the culture supernatant of transfected HepG2.2.15cells were measured by an enzyme-linked immunosorbent assay(ELISA)kit.The results showed that thethree plasmid-derived siRNAs and the synthetic siRNA can effectively reduce the quantities of HBs mRNAand protein.The plasmid-derived siRNA psiRNA1 was found to be the most effective inhibitor of HBsexpression.It can inhibit HBs-EGFP expression by 63.3% and suppress HBs mRNA by 75.6%.To furthersubstantiate the above observations,psiRNA1 was transfected into HepG2.2.15 cells(an HBV secreting cellline).The transfections resulted in almost complete blockage of HBsAg production,whereas control vector-transfected cells secreted high levels of HBsAg 7 days post-transfection.In conclusion,our data suggeststhat RNA interference(RNAi)is an efficient approach for reducing the level of HBs transcripts and proteinsand for suppressing HBsAg production. To study the inhibitory effects of plasmid-derived small interfering RNA (siRNA) andsynthetic siRNA on the expression of the hepatitis B virus surface (HBs) gene, three plasmid-derived siRNAs and one synthetic siRNA that complement the coding region of the HBs gene were prepared The HBs expression plasmid pHBs-EGFP was also constructed. HeLa cells were co-transfected with pHBs-EGFP and the above siRNAs. The HBs mRNA quantities were measured by reverse-transcription PCR, and the level of HBs-EGFP fusion protein was quantified by fluorescent microscope The concentrations of the hepatitis B virus surface antigen (HBsAg) derived from the culture supernatant of transfected HepG2.2.15 cells were measured by an enzyme-linked immunosorbent assay (ELISA) kit. These results showed that the plasmid-derived siRNAs and the synthetic siRNA can effectively reduce the amount of HBs mRNA and protein. The plasmid-derived siRNA psiRNA1 was found to be the most effective inhibitor of HBsexpression. It can inhibit HBs-EG FP expression by 63.3% and suppress HBs mRNA by 75.6% .To furthersubstantiate the above observations, psiRNA1 was transfected into HepG2.2.15 cells (an HBV secreting cellline). The transfections resulted in almost complete blockage of HBsAg production, but control vector-transfected cells secreted high levels of HBsAg 7 days post-transfection.In conclusion, our data suggest that RNA interference (RNAi) is an efficient approach for reducing the level of HBs transcripts and proteinsand for suppressing HBsAg production.