Organic/inorganic hybrid networks were prepared by a novel solvent-free two-step synthesis method. In the first step, prehydrolyzedcondensed reactive inorganic precursors (clusters) were prepared by a solgel process from monomeric alkoxysilanes with amino and glycido groups. The second step comprised their addition into epoxy resin and amine hardener, followed by the reaction of all components giving the final hybrid crosslinked materials. Their structure was evaluated by small-angle X-ray scattering, transmission electron microscopy, scanning electron microscopy, and dynamic mechanical and thermal analysis. The morphology of the organic/inorganic hybrid structures formed from glycidoprecursor revealed spherical silica-rich domains forming agglomerates with diameter from 100 to 500 nm. The aminoprecursor led to large highly condensed and branched silicon-rich structures. The organic/inorganic hybrid networks obtained from this precursor consisted of mixed siliconorganic phases covalently interconnected via epoxyamine bonds. Such hybrid networks showed significantly improved thermomechanical properties and better resistance against thermooxidation when compared with the neat epoxyamine network. Thin films as well as bulk materials were successfully prepared by this process. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012