The influence of the intracellular redox state on the hepatitis C virus (HCV) life cycle is poorly understood. This study demonstrated the anti-HCV activity of 2,3-dihydro-5-hydroxy-2,2-dipentyl-4,6-di-tert-butylbenzofuran (BO-653), a synthetic lipophilic antioxidant, and examined whether BO-653's antioxidant activity is integral to its anti-HCV activity. The anti-HCV activity of BO-653 was investigated in HuH-7 cells bearing an HCV subgenomic replicon (FLR3-1 cells) and in HuH-7 cells infected persistently with HCV (RMT-tri cells). BO-653 inhibition of HCV replication was also compared with that of several hydrophilic and lipophilic antioxidants. BO-653 suppressed HCV replication in FLR3-1 and RMT-tri cells in a concentration-dependent manner. The lipophilic antioxidants had stronger anti-HCV activities than the hydrophilic antioxidants, and BO-653 displayed the strongest anti-HCV activity of all the antioxidants examined. Therefore, the anti-HCV activity of BO-653 was examined in chimeric mice harboring human hepatocytes infected with HCV. The combination treatment of BO-653 and polyethylene glycol-conjugated interferon-α (PEG-IFN) decreased serum HCV RNA titer more than that seen with PEG-IFN alone. These findings suggest that both the lipophilic property and the antioxidant activity of BO-653 play an important role in the inhibition of HCV replication. J. Med. Virol. 85:241–249, 2013. © 2012 Wiley Periodicals, Inc.