AIM: To study the effect of Hepatitis C virus nonstructural 5A (HCV NS5A) on IFNα induced signal transducer and activator of transcription-1 (STAT1)phosphorylation and nuclear translocation.METHODS: Expression of STAT1 Tyr701 phosphorylation at different time points was confirmed by Western blot, and the time point when p-STAT1 expressed most, was taken as the IFN induction time for further studies. Immunocytochemistry was used to confirm the successful transient transfection of NS5A expression plasmid. Immunofluorescene was performed to observe if there was any difference in IFNα-induced STAT1 phosphorylation and nuclear translocation between HCV NS5A-expressed and non-HCV NS5A-expressed cells.Western blot was used to compare the phosphorylated STAT1 protein of the cells.RESULTS: Expression of HCV NS5A was found in the cytoplasm of PCNS5A-transfected Huh7 cells, but not in the PRC/CMV transfected or non-transfected cells. STAT1 Tyr701 phosphorylation was found strongest in 30 min of IFN induction. STAT1 phosphorylation and nuclear import were much less in the presence of HCV NS5A protein in contrast to PRC/CMV-transfected and non-transfected cells under fluorescent microscopy, which was further confirmed by Western blot.CONCLUSION: HCV NS5A expression plasmid is successfully transfected into Huh7 cells and HCV NS5A protein is expressed in the cytoplasm of the cells. IFN-α is able to induce STAT1 phosphrylation and nuclear translocation, and this effect is inhibited by HCV NS5A protein, which might be another possible resistance mechanism to interferon alpha therapy.