Abstract.A study is carried out to investigate the influences of compounding process and surface treatment on nanometre-sized TiO 2 filled polystyrene. The compounding process is discussed with a torque rheometer. The TiO 2 filler is surface-treated with a liquid titanate coupling agent. The effects of coupling agents on the mechanical, morphological, and thermal stability properties of TiO 2 /polystyrene(PS) nanocomposites were studied. Nanocomposites of different weight fractions are prepared, and their impact properties are evaluated. The unnotched impact strength increased. Surface treatment of TiO 2 filler generally yielded nanocomposites of higher impact strength than untreated system.