The surface properties and mixed micellization behavior of binary combinations of cationic gemini (C16-4-C16, 2Br−) tetramethylene-1,4-bis(cetyldimethylammonium bromide) with cationic monomeric surfactants viz. cetyltriphenylphosphonium bromide (CTPB), tetradecyltriphenylphosphonium bromide (TTPB), cetyltributylphosphonium bromide (CTBuPB), cetyldiethylethanolammonium bromide (CDEEAB) and tetradecyldiethylethanolammonium bromide (TDEEAB) have been investigated by surface tension and conductivity measurements in (10%, v/v) ethylene glycol mixture at 300 K. The critical micelle concentration (cmc), surface properties,  max (maximum surface excess), Amin (minimum surface area per molecule) and cmc (surface pressure at the cmc) have been determined. The deviation from the ideal of the mixed micelles has been discussed on the basis of Clint theory. The results of the mixed systems were analyzed in the light of the regular solution theory (Rubingh) and Rosen’s theory to evaluate the composition of the mixed micelle, the activity coefficient, the interfacial mole fraction of the surfactant at the mixed adsorbed film and the corresponding interaction parameters (ˇ and ˇ). The negative values of interaction parameters (ˇ and ˇ) for mixed micelle formation indicate the attractive interaction for all the system. The standard Gibbs free energies of adsorption (G◦ads), standard Gibbs free energies of micellization (G◦m), the excess free energies of micellization (Gex) and minimum free energy of the surface (G(s)min) of gemini with cationic monomeric surfactants were also evaluated. TheG◦ ads,G◦m and Gex values are negative indicating the spontaneity and stability of the mixed micelle.