The influence of fine SiC fillers (1 mu m) on ionic conductivity of (PEO)(16)LiClO4 electrolytes has been studied using impedance spectroscopy and differential scanning calorimetry. Small enhancement in the conductivity is observed for samples having SIC concentrations below 15 wt.%. Two antagonistic effects on the conductivity are observed, i.e. the decrease of the glass transition temperature, which enhances polymer chain motion, and the increase of the Volume fraction of the crystalline phase, which hinders the transport process. This observation suggests that it is the enhancement of the segmental motions of PEO that principally determines the ionic conductivity, while the increase in the conductivity is not large due to the increase of the crystalline phase. Measuring the thickness of specimens, the composite electrolyte is found to have a much better stiffness.