This study investigates the electrical behavior of silicon nitride/epoxy nanocomposites. It is demonstrated that the presence of the nanofiller affects the resin/hardener stoichiometry, which results in the development of different network structures throughout the matrix polymer. However, detailed analysis shows that this stoichiometric effect cannot account, alone, for the observed changes in the electrical behavior of the nanocomposite samples. A comparison between the electrical behavior of filled and the unfilled samples, where appropriate stoichiometric compensation has been applied, indicates that there is an additional effect that is exclusively a function of the nanofiller loading and which is superimposed on any matrix chemistry effects. Potential explanations for this nanoparticle effect are discussed, including: nanoparticle agglomeration; water shells around the nanoparticles; the influence of nanoparticles on matrix dynamics, structure or the free volume content of polymer interphase.