The micellization behavior of cationic gemini surfactants 1,3-bis(dodecyl-N,N-dimethylammonium bromide)-2-propanol [12-3(OH)-12,2Br -] and 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol [12-4(OH) 2-12,2Br -] have been investigated in binary mixed media of water and organic solvents [1,4-dioxane (DO) and ethylene glycol (EG)] by conductivity measurements. The micellization behavior in aqueous medium has been studied using conductivity, steady-state fluorescence, zeta potential and dynamic light scattering measurements. The process of micellization is delayed with increasing amount of an organic co-solvent, as a result, there is a progressive increase in critical micelle concentration (cmc), Gibbs free energy of micellization (ΔG o m) and Gibbs free energy of transfer (ΔG o trans). A good correlation between ΔG o m and Gordon parameters suggests that the cohesiveness of the mixture is reduced in presence of an organic co-solvent. Better proneness of micellization in EG as compared to that in DO as co-solvent is because of resemblance of EG with water. Also, the chemical structures of spacer group of gemini surfactants have shown a significant effect on the aggregation and the thermodynamic properties of micellization. The micellization of 12-4(OH) 2-12,2Br - is comparatively delayed than that of 12-3(OH)-12,2Br - in a given solvent system. The possible factors those can be responsible for the difference in cmc and that in ΔG o m between two studied geminis have been discussed. There is compensation between enthalpy and entropy for the formation of micellar aggregates. © 2012 Elsevier B.V. All rights reserved.