RNA interference (RNAi) has become a gold standard for validating gene function in basic life science research and provides a promising therapeutic modality for cancer and other diseases. This mini-review focuses on the potential of small interfering RNAs (siRNAs) in anticancer treatment, including the establishment and screening of cancer-associated siRNA libraries and their applications in anticancer drug target discovery and cancer therapy. This article also describes the current delivery approaches of siRNAs using lipids, polymers, and, in particular, gold nanoparticles to induce significant gene silencing and tumor growth regression.