It is intended to provide a polynucleotide that is resistant to RNase and has an RNA interference effect, etc. The present invention provides a single-stranded polynucleotide that is derived from a double-stranded polynucleotide comprising a sense strand polynucleotide corresponding to a target gene, and an antisense strand polynucleotide having a nucleotide sequence complementary to the sense strand polynucleotide, and has a structure in which the 5'-end of the antisense strand and the 3'-end of the sense strand are linked via a phenyl group-containing linker to form a phosphodiester structure at each of these ends.