Provided is a ribonucleoside derivative represented by General Formula (I): ##STR00001## (wherein R.sup.1 represents a hydrogen atom or the like, R.sup.2 represents a hydrogen atom or the like, R.sup.3 represents a methyl group or the like, and B represents a nucleic acid base residue optionally having a protecting group or a modifying group). An RNA containing this ribonucleoside derivative shows excellent hybridization ability and resistance to nuclease.