Small interfering RNA (siRNA) is yet a developing field in molecular biology and has unfolded as a novel post transcription gene silencing strategy which has therapeutic potentiality. Indeed They have been shown to play a vital role in a wide range of biological process. They regulate the expression of a larege number of mRNAs. The gene silencing mediated by this small RNA (siRNA) a major component of gene regulation during various developmental and physiological processes. The accumulating knowledge about their biogenesis and gene silencing mechanism will add a new dimension to our understnding about the complex gene regulatory networks. Every gene in human genome to a some extent contributing to a disease is amenable to regulation with siRNA, therefore opening an unprecedented opportunities for drug discovery. Besides the well established role for siRNA as a tool for target screening and validation in vitro, recent progress of siRNA delivery in vivo raised expectations for siRNA drugs as the up-and-coming 'magic bullet'. Whether siRNA compounds will make it as novel chemical entities from 'bench to bedside' will probably depend largely on improving their pharmaco kinetics in term