GW182 binds to Argonaute (AGO) proteins and has a central role in miRNA-mediated gene silencing. Using lentiviral shRNAinduced GW182 knockdown in HEK293 cells, this study identifies a new role of GW182 in regulating miRNA stability. Stably knocking down GW182 or its paralogue TNRC6B reduces transfected miRNA-mimic half-lives. Replenishment of GW182 family proteins, as well as one of its domain D12, significantly restores the stability of transfected miRNA-mimic. GW182 knockdown reduces miRNA secretion via secretory exosomes. Targeted siRNA screening identifies a 3 0 -5 0 exoribonuclease complex responsible for the miRNA degradation only when GW182 is knocked down. Immunoprecipitation further confirms that the presence of GW182 in the RISC complex is critical in protecting Argonaute-bound miRNA.