Recent progress in RNA biology has broadened the scope of therapeutic targets of RNA drugs for cancer therapy. However, RNA drugs, typically small interfering RNAs (siRNAs), are rapidly degraded by RNases and filtrated in the kidney, thereby requiring a delivery vehicle for efficient transport to the target cells. To date, various delivery formulations have been developed from cationic lipids, polymers, and/or inorganic nanoparticles for systemic delivery of siRNA to solid tumors. This review describes the current status of clinical trials related to siRNA-based cancer therapy, as well as the remaining issues that need to be overcome to establish a successful therapy. It, then introduces various promising design strategies of delivery vehicles for stable and targeted siRNA delivery, including the prospects for future design.