Provided is a single-stranded oligonucleotide that highly efficiently controls a target gene and can easily be produced. A single-stranded oligonucleotide expressed by formula (I), wherein X and Y hybridize using a first nucleotide sequence section and a second nucleotide sequence section. X has a first nucleotide sequence that consists of 7-100 nucleotides, includes at least one modified nucleotide, and can hybridize with a second oligonucleotide. Y has a second nucleotide sequence that consists of 4-100 nucleotides, allows hybridization with a first oligonucleotide, and includes at least one ribonucleotide. At least one of nucleotide sequences X, Xz, and Y has an antisense sequence that allows hybridization with a target RNA. At least one of L, Lx, and Ly is a linking group that includes a non-nucleotide structure.
