PROBLEM TO BE SOLVED: To provide an unnatural type oligonucleotide analog that has excellent antisense or anti-gene activity, is stable in vivo, and reduces the expression of side effects.SOLUTION: The present invention provides a nucleoside analog represented by the formula (1) or a salt thereof.SELECTED DRAWING: NoneCOPYRIGHT: (C)2016,JPO&INPIT【課題】優れたアンチセンス又はアンチジーン活性を有し、生体内で安定であり、副作用の発現の少ない非天然型のオリゴヌクレオチド類縁体を提供する。【解決手段】下記式(1)で表わされるヌクレオシド類縁体又はその塩。【選択図】なし