We have made a SiO2:PMMA hybrid nanocomposite based on 150nm spherical silica nanoparticles synthetized by sol-gel method. A molecule containing a methacrylate group (TPM), was chemically grafted to the silica surface to improve the electrical performance. The filling factor of the nanonanocomposite was up to 20%vol. The 1um thick nanocomposite films were deposited on polished steel by spin coating. Compared to similarly prepared PMMA films, the dielectric constant, as measured by BDS (proadband dielectric spectroscopy) was enhanced by a factor of two for the nanocomposite, and the disruptive electric field by a factor of 2.5. This eventually yields an overall improvement of the energy density by a factor of 12.5.