ZnO/polystyrene (PSt) composite nanoparticles with high grafting efficiency have been prepared by anchoring 4,4'-azobis(4-cyanovaleric acid) (ACVA) onto the surface of ZnO nanoparticles, and then exploiting its azo group to initiate polymerization of styrene monomer to synthesize composite nanoparticles. The polymerization mechanism of these ZnO/PSt composite nanoparticles with high graft efficiency is discussed. FTIR and XPS confirmed that ACVA had been covalently anchored on the surface of the ZnO nanoparticles via gamma-glycidoxypropyl trimethoxysilane. The anchoring percentage of ACVA on ZnO and the grafting efficiency of the ZnO/PSt composite nanoparticles were analyzed by thermo-gravimetric analysis (TGA), and were estimated as 17% and 85%, respectively. The effect of the amount of ZnO with anchored ACVA on conversion and grafting efficiency of styrene was also investigated. TEM proved the presence of ZnO nanoparticle appeared to be monodisperse in nanosize in polystyrene composite nanoparticles. SEM showed that ZnO nanoparticles could be homogeneously dispersed in PVC film by preparing surface-grafted ZnO/PSt nanopartides. The polymer chains grafted onto the nanoparticle surface enhanced the compatibility between the ZnO nanoparticles and PVC matrix. The PVC composite film presented a perfect anti-UV property, which can improve UV degradation resistance of PVC film. (C) 2011 Elsevier B.V. All rights reserved.