Nano-Al2O3 with an average size of 42 nm was prepared by pyrolysis method. PEO–LiClO4 based composite polymer electrolyte was prepared using solution cast technique. The samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and infra red (FT-IR) techniques. Effect of nano-Al2O3 ceramic filler concentration on the composite structure and its electrical properties (DC-conductivity, AC-conductivity, dielectric constant, dielectric loss and impedance) at a frequency and temperature ranges of 0–105 Hz and 293–323 K, respectively was studied. Melting temperature (Tm) of PEO decreased with addition of both LiClO4 salt and nano-Al2O3 filler due to increasing the amorphous state of polymer. All composite samples showed an ionic conductivity with the highest value for the sample containing 1.25 mol of nano-Al2O3. All results are correlated and discussed