The present invention relates to an RNAi-inducing nucleic acid molecule of novel structure which is able to penetrate into cells, and to a use therefor. More specifically, the present invention relates to a nucleic acid molecule of novel structure which is outstandingly efficient in suppressing a target gene even while being able to penetrate into cells without a separate cell delivery vehicle； the molecule being given a structure in which the phosphate backbone of at least one nucleotide contained in a double-stranded nucleic acid molecule that induces RNAi is substituted with phosphorothioate or phosphorodithioate, and to which a lipophilic compound is bonded. The present invention also relates to a method of suppressing the expression of a target gene by using the nucleic acid molecule. With the nucleic acid molecule structure according to the present invention, both cholesterol modification and phosphorothioate modification are introduced, and thus the molecule structure can maintain outstanding gene suppressing efficiency even while being able to penetrate into cells without a separate cell delivery vehicle, and the molecule structure can be delivered in sufficient amount for RNAi induction in the actual target site, and can resolve the problem of in vivo delivery which has previously proved to be problematical. Hence the nucleic acid molecule according to the present invention is useful in that the molecule can replace existing siRNA molecules and be actively used in cancer or viral infection therapy or the like in which siRNA has been used.La présente invention concerne une molécule d'acide nucléique, induisant de l'ARNi, de nouvelle structure, qui peut pénétrer dans des cellules, et son utilisation. Plus particulièrement, la présente invention concerne une molécule d'acide nucléique de nouvelle structure, qui est remarquablement efficace dans la suppression d'un gène cible, tout en étant capable de pénétrer dans des cellules sans véhicule séparé de distribut
