RNAi has rapidly become a powerful tool for drug target discovery and validation in an in vitro culture system and, consequently, interest is rapidly growing for extension of its application to in vivo systems, such as animal disease models and human therapeutics. Novel treatments and drug discovery in pre-clinical studies based on RNAi are currently targeting a wide range of diseases, including viral infections and cancers by the local administration of synthetic small interfering RNA (siRNA) that target local lesions. Recently, specific methods for the systemic administration of siRNAs have been reported to treat non-human primates or a cancer metastasis model. In vivo siRNA-delivery technology is a key hurdle to the successful therapeutic application of RNAi. This article reviews the non-viral delivery system of atelocollagen for siRNA, which could be useful for functional screening of the genes in vitro and in vivo, and will provide a foundation for further development of RNAi therapeutics.