RNA interference (RNAi) is a powerful tool in the study of gene function. We added poly(A) tails to the 3' ends of siRNA antisense strands by in vitro transcription, and investigated the silencing effects of poly (A)- tailed siRNAs on enhanced green fluorescence protein (EGFP) and red fluorescence protein (RFP) genes. The results of this study showed that siRNAs with single-stranded 3’-poly(A) tails at antisense strands had noticeably stronger silencing effect on exogenous reporter genes than their corresponding parental forms. The enhanced silencing effect appears to be related to the length of poly(A) but was non siRNA sequencespecific. Furthermore, our results demonstrate that weakly-activated PKR and reduced stability of mRNAs of exogenous reporter genes in vivo may be the possible mechanisms of this non-specific enhanced silencing effect. Our findings are likely to be of value in designing siRNAs with enhanced activity.