5'-Dimethoxytrityl-5-(3-methoxypropynyl)-2'-deoxyuridine phosphoroamidite was synthesized with the use of commercial 3- methoxypropyne. Oligonucleotides (ODNs) containing 5-(3-methoxypropynyl)-2'- deoxyuridine in different positions were prepared. The stabilities of the duplexes formed by these ODNs with the complementary templates are increased in comparison with the unmodified counterparts. On average modified residue incorporated, the Tm is raised by 1°C.