The behaviour of PEO8LiClO4 with different quantities of α-Al2O3 or γ-Al2O3 was investigated using DSC, AC conductivity and 7Li NMR experiments. DSC results showed that the presence of the filler does not change the glass transition temperature of the electrolyte but, on the other hand, modifies the quantity of its crystalline phase. From the AC impedance measurements, it was observed that the sample with the highest conductivity at room temperature is PEO8LiClO4 5.3 wt.% α-Al2O3. The change in the quantity of crystalline phase cannot alone explain the conductivity data, and it is suggested that the space charge contribution in the interphase of the filler particles and the polymeric chains influences the behaviour of the samples. The 7Li NMR results showed that line width narrowing begins at temperatures close to T g. From the hydrogen decoupling experiments it was possible to estimate the LiH average distances as 2.7 Å. The LiLi distance was calculated as being between 2.6 and 3.5 Å depending on the number of near neighbours lithium nuclei used in the model.