A post-synthetic reaction of 5-pivaloyloxymethyluridine (present in a support-bound RNA oligomer) with various nucleophilic reagents furnished efficiently the corresponding products bearing one of the tRNA wobble 5-methyluridines (mnm⁵U, cmnm⁵U, τm⁵U, nm⁵U, inm⁵U or cnm⁵U). The syntheses of oligoribonucleotides modified with inm⁵U and cnm⁵U are reported for the first time.