In order to improve the pharmacological properties of antisense and antigene oligonucleotides, oligodeoxynucleotides conjugated with amino sugars at the 5'-terminus were synthesized by solid phase fragment condensation (SPFC) method. The obtained DNA-sugar conjugates were evaluated in their chemical and biological activities to show that 5'-end modification of oligonucleotides with sugars enhanced the thermal stability of the hybrid duplex with complementary DNA, the resistance against nuclease digestion and the membrane permeability of the conjugates.