In this work, composite polymer electrolytes based on a thermoplastic polyurethane/LiClO4 amorphous system and on bare and functionalized zirconia nanoparticles as a filler are reported. The ceramic nanoparticles were synthesized via the sol-gel route using zirconium butoxide as the precursor for zirconium oxide nanoclusters and methacrylic acid as an organic modifier group. The salt concentration in the polymer phase was 17 wt% and fillers were added in the range between 2 and 10wt%. Scanning electron microscopy (SEM) was used to characterize the average size and the homogeneity of the nanoparticles in the polymer matrix, while impedance spectroscopy (IS) was used to evaluate the ionic conductivity of the composites. The addition of zirconia fillers results in an increase in ionic conductivity for all filled systems. The results also show that the functionalization of the zirconia nanoparticles promotes a significant increase in conductivity, suggesting that the interaction of the metracrylate-functionalized fillers with the polyurethane matrix was greatly improved. These results raise interest in the study of organically modified ceramic clusters as fillers for electrolyte polymers.