In the present work, the effect of inorganic fillers with different particle sizes on the composite polymer electrolytes consist of Polyethylene Oxide (PEO), Lithium Trifluoromethanesulfonate (LiCF3SO3) and Ethylene Carbonate (EC) has been explored. Composite polymer electrolytes have been prepared via solution-casting technique. Impedance spectroscopy was conducted at room temperature on the resulted electrolytes. FTIR and SEM/EDX analysis were carried out to further investigate the effect of fillers. Addition of the micron-range inorganic fillers into the polymer electrolyte film leads to an improvement in the ionic conductivity, i.e. from 1.701 × 10-5 S/cm to 2.970 × 10-5 S/cm (with addition of Al2O3) and 3.570 × 10−5 (with addition of SiO2). However, the conductivity was reduced when inorganic fillers with smaller particle size (i.e. nano-range) are employed. The SEM results showed that the filler was well distributed in the polymer matrix; the surface of electrolyte film became rougher after the addition of nano-range fillers. The interaction between PEO and additives was characterized by FTIR analysis to confirm the forming of the complexation.