Binding of cationic gemini surfactants alkanediyl-a-ω-bis(dimethyldodecylammonium bromides) with variable polymethylene spacer length ranging from 2 to 12 methylene groups to DNA in NaBr solution is investigated utilizing the tensiometry method. A simple method is presented for calculating the number of surfactant molecules bound to DNA. The results are evaluated in terms of the gemini surfactant spacer length, showing that gemini molecules with either short spacers (2 methylene groups) or long spacers are most efficiently adsorbed to DNA. A weak adsorption to DNA was found for gemini molecules with a medium spacer length (6 methylene groups in the spacer). The binding properties of cationic gemini surfactants as a function of spacer length are consistent with the results obtained by other experimental methods (dynamic light scattering measurements, fluorescence spectroscopy), indicating identical adsorption behaviour of gemini molecules as a function of the spacer length.