The present invention relates to an RNAi-inducing nucleic acid molecule having a new structure and the use thereof, and more particularly to a novel nucleic acid molecule having a structure comprising a first strand, which is 24-121 nt in length and comprises a region complementary to a target nucleic acid, and a second strand which is 13-21 nt in length and has a region that binds complementarily to the region of the first strand, which is complementary to the target nucleic acid, so that the nucleic acid molecule inhibits the expression of a target gene with increased efficiency, and to a method of inhibiting the expression of a target gene using the nucleic acid molecule. The nucleic acid molecule structure of the present invention increases the efficiency with which the nucleic acid molecule inhibits the target gene. Alternatively, the nucleic acid molecule of the present invention can either increase the ability of the siRNA to bind to the target gene or cause synergistic cleavage, by introduction of antisense DNA, antisense RNA, ribozyme or DNAzyme, thereby increasing the efficiency with which the nucleic acid molecule inhibits the target gene. In addition, when the nucleic acid molecule according to the present invention is used, the efficiency with which the target gene is inhibited can be maintained for an extended period of time. Accordingly, the RNAi-inducing nucleic acid molecule of the present invention can be effectively used for the treatment of cancer or viral infection in place of conventional siRNA molecules.
