4'-Alkoxy-oligothymidylates were prepared as model compounds to study the influence of a C4'-alkoxy group on hybridisation. The phosphodiester homooligomers (15 units long) containing either a 4'-methoxy or 4'-(2-methoxyethoxy) group were found to display increased hybridisation with both dA(15) and rA(15) complementary counterparts compared to the natural oligothymidylate. In addition, we found their hybridisation behaviour to be similar to that of the regioisomeric 2'-O-methyl-oligothymidylate. The formed complexes (duplexes and triplexes) were studied using UV spectroscopy and polyacrylamide gel electrophoresis (PAGE). Structural background of the hybridization behaviour was examined using NMR and MDS. The favourable hybridisation properties of the 4'-alkoxyoligothymidylates indicated that 4'-alkoxy modified nucleotides are promising compounds for the assembly of chimeric oligonucleotides with tunable properties.