Provided is a novel nucleic acid molecule that can be produced easily and efficiently and can inhibit the expression of a gene. The nucleic acid molecule is a single-stranded nucleic acid molecule including an expression inhibitory sequence that inhibits expression of a target gene. The single-stranded nucleic acid molecule includes: a region (X)； a linker region (Lx)； and a region (Xc). The linker region (Lx) is linked between the regions (Xc) and (Xc). The region (Xc) is complementary to the region (X). At least one of the regions (X) and (Xc) includes the expression inhibitory sequence. The linker region (Lx) has a non-nucleotide structure including at least one of a pyrrolidine skeleton and a piperidine skeleton. According to this single-stranded nucleic acid molecule, it is possible to inhibit the expression of the target gene.本發明之目的在於提供一種可抑制基因表現之新穎核酸分子，且該核酸分子可藉容易且有效率之製造方法來製造。即，製成一種單股核酸分子，其含有抑制目標基因表現之抑制表現序列，且特徵在於：包含區域(X)、連結區域(Lx)及區域(Xc)，前述區域(Xc)與前述區域(Xc)之間連結有前述連結區域(Lx)，前述區域(Xc)與前述區域(X)互補，前述區域(X)及前述區域(Xc)中之至少一者含有前述抑制表現序列，前述結合區域(Lx)具有非核苷酸結構，且該非核苷酸結構含有吡咯啶骨架及哌啶骨架中之至少一者。若以此種單股核酸分子，則可抑制前述目標基因之表現。
