The micellization of gemini surfactant pentamethylene-1,5-bis(tetradecyldimethylammonium bromide) (14-5-14) has been investigated in water and water-organic solvent mixed media (organic solvents used: 1,4-dioxane (DO), dimethylformamide (DMF), ethylene glycol (EG)). The conductivity in water and in mixed media (water + organic solvent) as a function of surfactant concentration was measured at different temperatures and the data were used to find critical micelle concentration (cmc) and degree of counterion dissociation (alpha) of the micelle. From the study, it is observed that the micellization tendency of the surfactant decreases in the presence of organic solvents and the increase in the cmc values is comparatively less below 20% (v/v) of organic solvents showing the predominance of water character in the bulk phase at lower compositions of the organic solvents. Thermodynamic parameters were also obtained from the temperature dependence of the cmc values. The standard free energy of micellization was found to be negative in all the cases that became less negative with the increase in the cosolvent content. (C) 2009 Elsevier Inc. All rights reserved.