As sugar-modified oligodeoxyribonucleotides, L-homooligomers (L-dA12 and L-dT12) and a L/D-alternative oligomer ((L-dA-D-dA)6) were synthesized. These oligomers were quite resistant towards phosphodiesterase degradations. L-dA12 formed complexes with poly(dT) and poly(U) at 0 degree C with different stabilities, on the other hand L-dT12 did not show obvious hypochromicities after mixing with complementary natural homopolymers. An alternative sequence, (L-dA-D-dA)6, interacted with both type homopolymers and stabilities of the complexes increased compared to that of L-dA12.