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In this work, the complex permittivity of epoxy resin is measured. Earlier, we have shown that the inclusion of nanometric alumina particles (Al2O3), both as-received and pre-processed, improves the ability of a polymeric dielectric (epoxy) to resist degradation when exposed to surface discharges. In this work, we use dielectric spectroscopy to characterize neat epoxy (unfilled) and epoxy nanocomposites prepared with as-received and pre-processed Al2O3 nanoparticles. The dielectric spectroscopy measurements and analyses are carried out in the frequency range of 10-3 Hz to 103 Hz and temperature range of 25degC to 90degC. Analyses of the data for neat epoxy indicate the presence of low frequency dispersion below 100 Hz. It is observed that the inclusion of nanoparticles lowers the effective real and imaginary permittivity of the composite material, at low temperatures. At higher temperatures, low permittivities are exhibited only by composites prepared with particles functionalized with silane before use. It is therefore seen that not only the presence of filler particles, but also the nature of the interface affects the dielectric properties.