Novel phosphorotioate DNAs (S-ODNs) bearing polyamine moiety at the C-5 position of 2'-deoxyuridine in place of certain thymidine residues and/or an acridine moiety at the 5'-terminus were prepared. The sequence of the S-ODNs is complementary to the rev region of HIV-1 mRNA. The duplexes consisted of the modified S-ODNs and the complementary DNA exhibited the enhanced stability compared to that consisted of the corresponding unmodified S-ODN and the complement. The improved antisense activity against HIV-1 was also observed for all modified S-ODNs.