A set of specimens consisting of an epoxy resin and ceramic SrFe12O19 nanoparticles were prepared varying the filler concentration. Specimens' morphology was examined by means of Scanning Electron Microscopy and x-Ray Diffraction spectra. Mechanical and thermal characterizations were conducted via Dynamic Mechanical Analysis and Differential Scanning Calorimetry respectively, in the temperature range 30-120 degrees C. Storage modulus increases substantially with filler concentration. The dielectric response of the nanocomposites was studied via Broadband Dielectric Spectroscopy in a wide frequency (10(-1)-10(7) Hz) and temperature (30-150 degrees C) range. Three relaxation processes were recorded in the spectra of all systems, attributed to both the filler and the polymer matrix. The energy storage efficiency of the prepared nanocomposites was examined in terms of the energy density as a function of temperature, frequency and filler concentration. Finally, a novel method for the determination of the real part of dielectric permittivity of the nanocomposites' interface is developed and tested. (C) 2017 Elsevier Ltd. All rights reserved.