This paper reports the conductivity and DSC measurements of composite electrolytes containing the PEO:LiBF4 complex, and TiO2 and ZrO2 nanosized particles. Below the melting temperature of PEG, conductivity is strongly dependent upon thermal history. The roles of the ceramic phase are to depress the melting temperature and retard the kinetics of crystallization of PEG. This results in a conductivity relaxation below the melting temperature of PEO which appears to be a characteristic of these composite electrolytes.