Organic-inorganic hybrid materials synthesized by the sol-gel process have been developed for several years. This synthesis method can effectively overcome the defects of conventional composite materials. In this investigation, epoxy/SiO2 hybrid material was synthesized by a sol-gel process with a precursor system. Tetraethoxysilane, water, and ethanol were mixed in appropriate proportions, varying the amounts of catalyst, alkalinity, and acidity, and then processed by a hydrolysis-condensation reaction at room temperature. The product synthesized with this process is called a precursor. The coupling agent gamma-glycidoxypropyl-methyldiethoxysilane (KBE-402) was used to modify the surface of the silica. The role of the coupling agent was to add covalent bonding between epoxy resin and silica, which reinforced the interfacial force of the hybrid material. The epoxy resin was mixed with precursor in different proportions and then cured at 170degreesC for 1 h. The thermal property of the epoxy/SiO2 hybrid materials was studied by thermogravimetric analysis and DSC. From the results, we found the precursor prepared with acidity catalyst was better than that prepared with alkalinity catalyst. Coupling agent improved the thermal property of epoxy/SiO2 hybrid materials, especially when the temperature was high and the suitable amount of the coupling agent for the hybrid system was 5%. The glass-transition temperature of the hybrid materials was increased to adapt to the content of precursor from 80 to 113degreesC. (C) 2003 Wiley Periodicals, Inc.