The paper presents the analysis of micellization behavior of cationic gemini surfactants with similar structures with varying atom number in spacer: heptylene-1,7-bis(dimethyloctylammonium) bromide (8–7–8) and octylene-1,8-bis(dimethyloctylammonium) bromide (8–8–8) in water and water–ethanol solvent mixed media. Experiments were carried out by using conductometric method within the temperature range of 288.15–323.15 K. The values of micellization parameters and thermodynamic functions of aggregation [critical micelle concentration (cmc), the degree of dissociation of micelles (α), enthalpy of micellization (ΔHmo), entropy of micellization (ΔSmo), Gibbs free energy of micellization (ΔGmo] within the temperature range investigated were determined. Based on the investigations performed it has been shown that the systems containing the additives ethanol have a positive value ΔGtranso, a more positive value ΔGmo, and a higher value of α and cmc as compared to pure water what confirms that the micellization pro...