RNA interference (RNAi) is a powerful endogenous process initiated by short double stranded RNAs, which results in sequence-specific posttranscriptional gene silencing. Because any protein that causes or contributes to a disease is susceptible to RNAi, the RNAi has high potential for therapeutic treatments. In a clinical setting, however, there are many obstacles to targeted delivery of small interfering RNA (siRNA) in vivo, specificity and stability of the RNAi reagents. In this review, we focus on recent progress in the development of efficient siRNA delivery vehicles to help the application of siRNA to in vivo therapy.