The conductances of cetylpyridinium chloride (CPyCl)–tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of CPyCl (x_CPyCl) have been measured in water, ethylene glycol–water (EG–W) and diethylene glycol–water (DEG–W) mixtures consisting of 20, 40 and 60 wt.% EG and DEG in their respective binary mixtures at 30 °C. From the conductivity data, the mixed critical micellar concentration (cmc), degree of counter-ion dissociation (χ), standard Gibbs energy of transfer of the surfactant hydrocarbon chain from medium to the micelle (ΔG_HP^°), and Gibbs energy of transfer of surface contributions (ΔG_s^°) for mixed micelles were computed. The non-ideality in the mixed micelle formation was evaluated by using the regular solution theory extended by Rubingh. It was observed that the non-ideality decreases with increase in the amount of EG or DEG. This was attributed to the solvation of the surfactant hydrophobic tail by EG or DEG molecules owing to EG or DEG–hydrocarbon interactions.