To investigate the interfacial effect on properties of epoxyacrylatesilica composites, submicron-sized silica spheres were synthesized by solgel reaction under a basic environment and their surfaces were endowed with vinyl functional groups by further modification with 3-methacryloxypropyl trimethoxy silane. The pure silica (PS) and the modified silica (MPS) spheres were characterized by Fourier transform infrared, 29Si- and 13C-nuclear magnetic resonance (NMR), scanning electron microscope (SEM), and particle size analyzer. The silica spheres were then added to the presynthesized difunctional epoxyacrylate resin with one vinyl group and one epoxide group at each end, in addition to the photo- and thermo-curing agents. After cure, thermal and mechanical properties of the obtained epoxyacrylatesilica composites were measured and compared. Tensile mechanical properties including initial modulus, ultimate tensile strength, and elongation at break, as well as the fracture energy of the epoxyacrylatesilica composite were all increased by increasing the content of silica spheres. Moreover, the composites filled with MPS had stronger interfacial strength between silica sphere and matrix than those with PS and thus exhibited an additional increase of tensile mechanical properties and fracture toughness. The increase of fracture toughness was owing to the crack deflection and particlematrix debonding as evidenced by SEM pictures on the fracture surface. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers