Analogues of oligonucleotides and mononucleotides with hydrophobic and/or cationic phophotriester functionalities often generate an improvement in target affinity and cellular uptake. Here we report the synthesis of phosphotriester oligodeoxyribonucleotides (ODNs) that are stable to the conditions used for their preparation. The method has been demonstrated by introducing phosphoramidite synthons where N-benzyloxycarbonyl (Z) protected amino alcohols replace the cyanoethyl group. After synthesis these ODNs were found to be stable to the condition required to remove base labile protecting groups and the ODNs from the solid support. Moreover the use of 1-(4,4-dimethyl-2, 6-dioxocyclohex-1-ylidene) ethyl (Dde) in place of Z protection on the amino alcohol has allowed us to introduce cationic aminoethyl phosphotriester modifications into ODNs. Melting temperatures of duplexes containing cationic or hydrophobic Z modified ODNs indicate that the backbone-phosphotriester modifications minimally affect duplex stability. Nuclease stability assays demonstrate that these phosphotriesters are resistant toward 5'- and 3'-exonucleases. Fluorescently labeled 23-mer ODNs modified with four cationic or hydrophobic Z phosphotriester linkages show efficient cellular uptake during passive transfection in HeLa and Jurkat cells.