The present inventors focused on siE sequences that have been thought to show RNAi activity against HCV viral RNAs, and mainly selected the D5-50 and D5-197 regions present within the IRES region, and carried on the analysis. As a result, the present inventors successfully identified siRNA sequences that exhibit a more effective RNAi activity against hepatitis C virus RNAs. Furthermore, the siRNAs were demonstrated to have a significant inhibitory effect on HCV propagation in an in vivo system.