The present invention provides a novel artificial mimic miRNA utilizing miRNA. An artificial mimic miRNA is a single-stranded nucleic acid including: a X region and a Y region, the Y region and the X region being linked, wherein the X region is a guide strand sequence of a mature miRNA or a partial sequence of the guide strand sequence of the mature miRNA and consists of a linking side region (X B ) and a non-linking side region (X F ) to the Y region, the linking side region (X B ) is a sequence that does not cause intramolecular annealing within its region, and the Y region is a sequence that intramolecularly anneals to the non-linking side region (X F ) of the X region. According to the artificial mimic miRNA of the present invention, the expression of the target gene can be inhibited.
