Double-stranded DNA is one of the most important intracellular targets of anticancer agents. Damage of DNA structure or functions can disturb transcription and/or translation processes, thus inducing the death of tumor cells. In this study, the formation of a complex between a novel dimeric bisbenzimidazole DB(7) and a poly(dA-dT) duplex was investigated compared to a known monomeric bisbenzimidazole MB(Ac). The DB(7)-poly(dA-dT) binding constant determined by fluorescence spectroscopy using a Scatchard plot was 1.18 х 10⁸ M^-1, which is two orders of magnitude higher than the respective binding constant for MB(Ac) (2.06 х 10⁶ M^-1). Thus, our findings suggest that the presence of two bisbenzimidazole moieties in the ligand structure significantly increases its affinity to the polynucleotide, which motivates the synthesis of new potential anticancer drugs based on dimeric bisbenzimidazoles.