This paper deals with the synthesis of m 3 2 , 2 , 7 G 5 ' pppAmpUmpApd(CpTpTpApCpCpT), a 5'-TMG-capped RNA-DNA chimeric oligonucleotide, which is expected to be conveyed to the nucleus by snurportin 1, a nuclear-transport protein. This 5'-TMG-capped RNA-DNA chimeric molecule was synthesized by the enzymatic condensation of m 3 2 , 2 , 7 G 5 ' pppAmpUmpA with A 5 ' ppd(CpTpTpApCpCpT) in the presence of RNA ligase. An inherent serious side reaction was disclosed in the 5'-adenylation of d(CpTpTpApCpCpT) on the solid support, but the use of an active ester intermediate as the pA donor gave an improved result.