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.本發明為提供一種可高效率地控制標的基因而可容易地製造之單股寡核苷酸。 本發明的單股寡核苷酸為，式(I)所示的X與Y在第一核苷酸序列部分與第二核苷酸序列部分進行雜交的單股寡核苷酸。X係由7～100個核苷酸所成，含有至少1個修飾核苷酸，具有可進行與第二寡核苷酸的雜交之第一核苷酸序列。Y係由4～100個核苷酸所成，可進行與前述第一寡核苷酸之雜交，具有含有至少1個核糖核苷酸之第二核苷酸序列。核苷酸序列X、Xz及Y的至少一個為具有可進行與標的RNA之雜交的反義序列。L、Lx及Ly的至少1個為含有非核苷酸結構之連結基。
