Provided is a single-stranded oligonucleotide capable of controlling a gene of interest at high efficiency and being produced easily. A single-stranded oligonucleotide represented by the formula X-L-Y in which X and Y hybridize with a first nucleotide sequence portion and a second nucleotide sequence portion. X comprises 7-100 nucleotides, includes at least one modified nucleotide, can hybridize with a second oligonucleotide, and has a first nucleotide sequence including at least four consecutive nucleotides recognized by RNase H. Y comprises 4-100 nucleotides, can hybridize with the first oligonucleotide, and has a second nucleotide sequence including at least one ribonucleotide. Nucleotide sequence X and/or Y has an antisense sequence that can hybridize with an RNA of interest. L is a group derived from a third oligonucleotide that is degraded under physiological conditions.提供一種高效率地控制標的基因，且可容易製造之單股寡核苷酸。以式X-L-Y所表示，X與Y為以第一核苷酸序列部分與第二核苷酸序列部分雜交的單股寡核苷酸。X係由7~100個核苷酸所構成，包含至少1個修飾核苷酸，可與第二寡核苷酸雜交，具有包含被RNaseH辨識之至少4個連續的核苷酸的第一核苷酸序列。Y係由4~100個核苷酸所構成，可與前述第一寡核苷酸雜交，具有包含至少1個核糖核苷酸的第二核苷酸序列。核苷酸序列X及Y之至少一者具有可與標的RNA雜交之反義序列。L係源自在生理條件下被分解之第三寡核苷酸的基。
