A series of polystyrene/silica nanocomposites with different inorganic nanofiller content were prepared by evaporating of toluene solvent. The weight fraction of silica nanoparticles of an average diameter of 7 nm treated with hexamethyldisilazane was varied (2, 5, 10, 15 and 30 wt.%). The polystyrene nanocomposite morphology was studied by scanning electron microscopy. The thermal stability of the samples was determined using thermogravimetry, coupled with differential scanning calorimetry. The influence of the filler content on glass transition temperature of polystyrene/silica nanocomposites was followed by differential scanning calorimetry. It was found that the polystyrene glass transition temperature was influenced by the hydrophobic silica content. A mathematical method to describe the glass transition temperature dependence on the polystyrene/silica ratio is proposed. According to the experimental results and calculations, the highest thermal stability of the nanocomposite belongs to 18% silica content. (C) 2010 Elsevier B.V. All rights reserved.