Conserved in many eukaryotic cells, RNA silencing is a mechanism that suppresses gene expression through RNA-mediated sequence-specific interactions. In plants, RNA silencing plays an important role against virus infection. A counter-defensive strategy in plant viruses has evolved by encoding suppressor proteins to overcome RNA silencing. Up to date, over twenty suppressors encoded by plant, animal and human viruses had been identified. A hot topic in virology has been focused on the identification of suppressors of RNA silencing and the mechanism for inducing silencing. The discovery and identification of viral suppressors of RNA silencing, possible mechanisms involved in RNA silencing suppression and its relationship with symptom formation of viral diseases, and suppressors of animal viruses were reviewed. The applications of these suppressors in plant biological and biotechnological research were also discussed.