Detailed investigations of a new Ag+-ion-conducting two-phase composite electrolyte system (1 - x) (0.75Agl:0.25AgCl) : xSnO(2) are reported, where 0 less than or equal to x less than or equal to 50 in weight per cent. A "quenched-and-annealed (0.75Agl:0.25AgCl) mixed system-solid solution" was used as the first phase instead of the commonly used host matrix salt Agl. Micron-sized particles (about 10 mu m) of SnO2 were dispersed in the first (matrix) phase. The composition 0.8(0.75Agl : 0.25AgCl):0.2SnO(2) exhibited conductivity enhancements of more than eight times over the annealed host and about three times over the quenched host at room temperature and has been referred to as "optimum composition". The existence of two separate phases has been ascertained by X-ray diffraction and differential thermal thermal analysis techniques. The temperature dependence of the electrical conductivity, sigma, ionic mobility, mu, mobile ion concentration, n, ionic transference number, t(ion), and ionic drift velocity, V-d, are also reported. The enhancement in the conductivity in this two-phase composite electrolyte has been attributed to the increase in ionic mobility at room temperature.