Abstract: Objective To investigate the effects and regulation mechanism of HCV core/NS3/NS5A on expression of IFN-β in HepG2 cells. Methods HCV core/NS3/NS5A proteins were cloned (pcDNA3.1/myc-His-core/NS3/NS5A) and expressed in HepG2 cells, then the expression level of IFN-β was detected by qRT-PCR, Western blot hybridization and ELISA. IFN-β promoter reporter vector (PGL4.10-IFN-β-P) was constructed and used for regulation mechanism study by luciferase assay. Results HCV core/NS3/NS5A proteins were successfully expressed in HepG2 cells post-transfection. Both the mRNA level and protein expression of IFN-β were significantly decreased (P ＜ 0.05) in the presence of NS3/NS5A protein. Luciferase assay revealed that NS3 /NS5A proteins downregulated IFN-β promoter activity (P ＜ 0.05). Meanwhile, HCV core protein had no significant effect on IFN-β expression. Conclusions Overexpression of NS3/NS5A could inhibit the expression of IFN-β by downregulating IFN-β promoter activity.