The increased use of nanoparticles as performance-enhancing fillers in resins for industrial applications has stimulated research for the modification of the nanoparticles’ surfaces. The modification of the surface of inorganic nanoparticles is a key strategy to ensure compatibility of the particles with the polymer matrix and to avoid aggregation of nanoparticles. In this work, inorganic nanoparticles (in particular boron nitride and silica nanoparticles) were embedded into an epoxy/anhydride polymer matrix, and the effect of nanoparticles on thermo-mechanical as well as thermal properties and the curing of the thermoset were determined. Modification of the nanoparticles has been achieved by reaction of surface OH-groups with silanes. Characterization of the surface modification has been performed by FT-IR spectroscopy, contact angle measurement, pyrolysis mass-spectroscopy and thermo-gravimetric analysis, respectively. Moreover, electron microscopy images show the distribution of the modified nanofillers within the polymer matrix. The curing behavior of the thermoset and the properties of the nanocomposites compared to the neat resin have been studied with respect to surface modification and particle concentration. The different properties of the nanocomposites compared to those of neat resin can be correlated to the presence of nanoparticles and interactions of the polymer with the dispersed particles. Differences in mechanical and thermal properties become more pronounced with the addition of nanoparticles to the polymer matrix; this is due to altered curing behavior of the nanoparticle-filled polymer matrix compared with pure resin. The research work was performed within the K-Project “PolyComp” at the Polymer Competence Center Leoben GmbH (PCCL, Austria). Funding is provided by the Austrian Government and the State Government of Styria.