In this research, hybrid materials based on poly(methyl methacrylate) and silica were synthesized via sol-gel process. Their glass transition behavior was investigated by differential scanning calorimeter. In DSC measurement, 180 degreesC heat-treated hybrid materials exhibited higher miscibility as compared to untreated materials. Relationship between miscibility variation of hybrid materials and heat treatment was discussed with the data From thermogravimetric analysis and infrared spectra. It was found that degradation behavior and silica structure was affected by heat treatment. At the same time, content of hydrogen bonds were elevated at the organic-inorganic interface, which may enhance the phase miscibility. (C) 2001 Elsevier Science Ltd. All rights reserved.