Novel nucleoside derivatives represented by the following general formula (1): wherein X is(are) the same or different and each represents a pyrimidine or purine base or a derivative thereof, Y and Y′ are the same or different and each represents at least one amino acid or amino acid derivative selected from the group consisting of serine, threonine, ornithine, aspartic acid, glutamic acid, lysine, arginine, cysteine, methionine, δ-hydroxylysine, N-aminoethylglycine, N-aminoethylserine, N-aminoethyllysine, N-aminoethylornithine, N-aminoethylaspartic acid, N-aminoethylglutamic acid, homoglutamic acid, β-thiocarbonylaspartic acid, γ-thiocarbonylglutamic acid, and δ-thiocarbonylhomoglutamic acid, R1 represents a hydrogen atom or a hydroxyl group, A represents a single bond or a carbonyl or thiocarbonyl group, 1 is an integer of 0 to 5, and n is an integer of 1 to 100.