Polymer-grafted nanosilica hybrid composites which possess a hard backbone of nanosilica and a soft shell of brush-like poly(styrene-co-maleic anhydride) (PSMA) were prepared via "grafting onto" strategy based on nitroxide-mediated radical polymerization (NMRP) using 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as mediator. Two steps were used to graft styrene/Maleic anhydride copolymer chains to the surface of nanosilica: anchoring of vinyl trimethoxysilane(A-171) onto the surface of nanosilica firstly, and then using TEMPO as radical trap, trapping the radicals produced by reaction of benzoyl peroxide (BPO) with styrene, Maleic anhydride and the vinyl group in grafted A-171 molecules. Finally, well controlled molecular weight (M-n) and narrow molecular weight distributions (M-w/M-n) of PSMA chains were grown from the surface of nanosilica. The prepared SiO2-g-PSMA hybrid particles have been extensively characterized by FT-IR, XPS, TGA, TEM, respectively. (C) 2008 Elsevier Ltd. All rights reserved.