Epoxy/alumina nanocomposites of various compositions were prepared by dispersing modified and nonmodified boehmite nanoparticles in diglycidyl ether of bisphenol-A using diethylenetriamine as curing agent. Measurements of the viscosity of the nanodispersions provided information on particle-particle and particle-resin interactions. The structure of the nanocomposites was studied by scanning electron microscopy on fractured samples. Effects of nanoparticles on polymer dynamics was studied in detail by dynamic mechanical thermal analysis and two dielectric techniques, broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents. Three secondary relaxations, c, b, and x, the segmental a relaxation associated with the glass transition, and an interfacial relaxation, in the order of increasing frequency/decreasing temperature, were observed and studied. A correlation between viscosity (of the nanodispersions), storage modulus, glass transition temperature, real part of dielectric permittivity, and ductility of the nanocomposites was observed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3613-3627, 2011