In situ synthetized silver-photocurable epoxy resin nanocomposites were analyzed by dielectric spectroscopy to study the local dynamics at temperatures well below the glass-transition temperature and the effect of silver nanoparticles on them. Two secondary processes, beta and gamma, were detected both for the neat matrix and nanocomposites. Relaxation times of the beta secondary relaxation, obtained by fitting to Havriliak-Negami equation, were lower in the nanocomposites, as well as the activation energies calculated from the Arrhenius temperature dependence of relaxation times, due to the plasticization effect of the trapped solvent. The electric modulus formalism was used to detect the interfacial or MWS polarization, present both in the neat matrix and in the nanocomposites due to heterogeneities and interfaces. The activation energy of this relaxation increased with nanoparticle content, thus indicating an increase of the heterogeneities due to the nanoparticles. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2361-2367, 2011