The composite solid electrolytes RbCl-x mole percent (m/o) Al2O3 (0 less than or equal to x less than or equal to 50) prepared by conventional powder metallurgy and solution casting processes, have been investigated by impedance analysis x-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM). The composites prepared by the former method exhibit about an order of magnitude lower conductivity than those prepared by the latter technique. The XRD and DTA results show that no phases other than RbCl and Al2O3 are present in the composites. SEM results show that RbCl grains are interspersed with Al2O3 particles. The conductivity of dispersed systems depends on the processing, particle size, and concentration of Al2O3. The mechanism of enhanced conductivity is proposed to be the generation of excess Rb+ ion vacancies in the host matrix at the matrix-particle interface. Macroscopically the results are explained satisfactorily on the basis of random resistor network model by assuming the formation of high conducting space charge layer along the matrix-particle interface.