As microRNA silencing processes are mediated by the protein Argonaute 2 and for target RNA binding only a short sequence at the microRNA's 5' end (seed region) is crucial, we report a novel inhibitor class: the microRNA-specific Argonaute 2 protein inhibitors that not only block this short recognition sequence but also bind to the protein's active site. We developed a model for rational drug design, enabling the identification of Argonaute 2 active site binders and their linkage with a peptide nucleic acid sequence (PNA), which addresses the microRNA of interest. The designed inhibitors targeting microRNA-122, a hepatitis C virus drug target, had an IC50 of 100 nM, 10-fold more active than the simple PNA sequence (IC50 of 1 μM), giving evidence that the strategy has potential. Due to their lower molecular weight, these inhibitors may show better pharmacokinetic properties than reported oligonucleotide inhibitors, enabling them for potential therapeutic use.