Small RNAs play a critical role in the regulation of gene expression in diverse cellular processes. This mechanism, termed RNA silencing or RNAi, also functions as a defense mechanism against molecular parasites such as virus and transposon. Whereas RNA silencing is triggered by viral infection, viruses suppress RNA silencing to establish infection, and sometimes even exploit it for their infection. In this mini review, we describe intimate interactions between viruses and host organisms in RNA silencing.