Abstract: Objective To explore advantage of RNA guiding activity in vitro cleavage assay and intracellular antiviral effects for hepatitis C, basing on one External Guide Sequence (EGS)sequence of the conserved region of 5’UTR of HCV genome. Methods We analyzed the sequence and structure of the conserved region of 5’UTR of HCV genome with computer software and designed one External Guide Sequence (EGS) which was direct at the potential targeting site (C67-G68). We tested the gene expression of HCV in Northern blot and Western blot and its antiviral activity by fluorescence quantitative PCR in the Huh7.5.1 cell which was transfected by EGS-C67. Results EGS-C67 had obvious advantage of RNA guiding activity in vitro cleavage assay. Our results indicated that EGS-C67could obviously inhibit the gene expression of HCV and inhibit the proliferation of HCV and down-regulate the titer of HCV about 150 times（p＜0.01）. Conclusions EGS-C67 , the new antiviral RNA has notably antiviral activity in cultured cells , thus could provide a new promising approach for development of anti-HCV strategy.

Key words: HCV, external guide sequence , antiviral