The mixed micelle formation of binary cationic 14-s-14 gemini with conventional single chain surfactants was studied by conductivity measurements. The critical micelle concentration (cmc) and the degree of counterion binding values (g) of the binary systems were determined. The results were analyzed by applying regular solution theory (RST) to calculate micellar compositions (X), activity coefficients (f1, f2), and the interaction parameters (β). The synergistic interactions of all the investigated cationic gemini+conventional surfactant combinations were found to be dependent upon the length of hydrophobic spacer of the gemini surfactant. The excess Gibbs free energy of mixing was evaluated, and it indicated relatively more stable mixed micelles for the binary combinations.