Ac conductivity studies carried out over a temperature range of 0-100 degrees C for polymeric electrolytes from the PEO-LiClO4-alpha-Al2O3 system are reported. Electrolytes of various salt concentrations and containing 15 mass% alpha-Al2O3 are studied. The contribution of charge carrier concentration and ion mobility to the de ionic conductivity of these composite polymeric electrolytes is discussed. A change in the temperature dependence of ionic conductivity is observed around the melting point of the crystalline phase of the composite electrolytes. An increase in dielectric constant following this phase transition is also observed. Above the melting temperature, an increase in the conductivity depends either on an increase in ionic mobility (samples with low salt concentration) br on the creation of charge carriers (samples with high salt concentration).