Optical, electrical, and thermal properties of hybrid polymer thin films, made of poly(ethylene oxide) (PEO) filled with electrolyte alum salt of different concentrations, and doped with conductive carbon black (CB) nanoparticles (0.1 wt%), have been investigated. The optical properties were studied in the UV-visible wavelength range, thermal properties were studied as a function of temperature, filler content, and applied field frequency. The observed physical constants of the casted thin films like optical energy gap, energy tails, refractive index, thermal conductivity, impedance, dielectric constant, and electric modulus were determined. It was found that these measured quantities vary with the incident UV-wavelength, alum content, temperature and applied field frequency. The dependence of the electric modulus on frequency exhibit a relaxation peak occurs at 600 kHz.