Both unmodified cupric oxide (CuO) nanoparticles and those functionalized with a bi-functional coupling agent methacryloxypropyl-trimethoxysilane (MPS) were used to fabricate vinyl-ester resin polymeric nanocomposites. The nanoparticle functionalization was observed to have a significant effect on the physical properties of the cupric oxide filled vinyl-ester resin nanocomposite. Thermal degradation study by thermo-gravimetric analysis (TGA) showed the increased thermo-stability in the functionalized-nanoparticle-filled vinyl-ester resin nanocomposites as compared with the unmodified-nanoparticle-filled counterparts. The more uniform particle dispersion and the chemical bond between nanoparticle and vinyl-ester resin were found to contribute to the increased thermal stability and enhanced tensile strength.