Epoxy resin-grafted SiO2 nanoparticles stabilized in toluene were successfully designed by the simultaneous surface modification of SiO2 nanoparticles during bead milling which involves the adsorption of polyethyleneimine-oleic acid complex (PEI-OA) and epoxy resin grafting to the free amine groups of PEI-OA (PEI-OA-Epoxy). The effectiveness of epoxy grafting on the properties of the SiO2/epoxy based nanocomposites were investigated using a bead-milled SiO2/toluene suspension stabilized with PEI-OA, PEI-OA-Epoxy, and a complex of PEI and an anionic surfactant comprising an epoxy-soluble polyethylene glycol-based chain (PEI-AS). While SiO2 nanoparticles were pulverized with similar sizes (c.a. 126-171 nm) and stabilized in toluene with any of the three surface modifications, PEI-OA-stabilized SiO2 nanoparticles aggregated during processing epoxy-based composites. PEI-AS-and PEI-OA-Epoxy-stabilized SiO2 nanoparticles maintained their dispersion stability, however, the epoxy composites with PEI-OA-Epoxy-stabilized SiO2 nanoparticles exhibited better material properties, such as increase in the strain at fracture and higher T-g. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.