Several oligodeoxyribonucleotides containing viologen derivatives in the form of covalent linkage at the specific site of the phosphorous backbone, were synthesized and characterized. Incorporation of the viologen molecule into DNA oligomer was confirmed by the P-31-NMR, PAGE analysis and enzymatic degradation reaction, and ultraviolet, ESR spectra of the derived cation radicals. Judging from the Tm values and CD spectra, the hybridization does not distort the duplex with the complementary strand to a great extent.