The conduction characteristics of CsCl-Al2O3 composite solid electrolytes prepared by conventional as well as by solution casting methods have been studied by complex impedance analysis, DTA, XRD techniques. The composites prepared by the solution casting method exhibit higher conductivity values than those prepared by the conventional method. XRD and DTA results show that no phases other than CsCl and Al2O3 are present in the composites. The conduction mechanism is proposed to be the generation of excess chloride ion vacancies in the host matrix at the matrix-particle interface. Though the well known B2(CsCl structure) --> B1 (NaCl structure) phase transition in CsCl is detected by the DTA of CsCl-Al2O3 composites, it is conspicuous by its absence in the log (sigmaT) versus I/T plots. This apparent suppression of B1 --> B2 transition in the CsCl-Al2O3 composites has been attributed to the fact that the conduction in composites is dominated by the migration of chloride ion vacancies in the space charge region at the matrix-particle interface.