The synthesis of silica-graft acrylonitiile-butadiene-styrene (ABS) nanocomposites and their thermal properties are studied. The silica nanopowders are treated with silane to introduce reactive groups onto the silica surfaces. The dispersion of modified silica nanoparticles in tetrahydrofuran (THF) is significantly improved. The silica-graft ABS composites were prepared by an open ring reaction and radical grafting copoly-merization of modified silica, styrene, and maleic anhydride (MAH) in ABS/THF solution. Differential scanning calorimetry (DSC) results show that the glass transition ternperature (T-g) of ABS-graft-SiO2 shifts obviously to high temperatures with increasing silica content. The TGA results indicate that the thermal stability is also improved with the increase of grafted silica. (C) 2004 Society of Plastics Engineers.