The mixed micellar properties of two cationic gemini surfactants, alkanediyl-alpha,omega-bis(tetradecyldimethylammonium bromide) and alkanediyl-alpha,omega-bis(hexadecyldimethylammonium bromide), 14-s-14 and 16-s-16, in aqueous solution have been investigated by conductivity and fluorescence techniques. The conductivity method has been carried out to evaluate critical micelle concentration (c), degree of counterion binding (g), and other related parameters like ideal mixed critical micelle concentration (c*), micellar mole fraction (x), interaction parameter (beta) from Rubingh's model, and x(ideal) from Motomura's model. Activity coefficients (f(1) and f(2)) and Gibbs excess energy (G(E)) were also calculated. Fluorescence measurements were used to obtain the values of N(agg) and Stern-Volmer constant (K(sv)). The results suggest synergism in the system. The beta values are negative, and their magnitudes increase with increasing spacer chain lengths. x(1) > x(1)(ideal) values suggest that the contribution of the 14-s-14 component is greater as compared to that in the ideal state.