Abstract ZnO nanoparticles were synthesized by homogeneous precipitation. To reduce the aggregation among ZnO nanoparticles, an effective surface modification method was proposed by grafting polymethyl methacrylate (PMMA) onto the ZnO particles. That is, the surface of ZnO nanoparticles was firstly treated with a KH570 silane coupling agent, which introduces functional double bonds onto the surface of ZnO nanoparticles, followed by radical grafting polymerization in non-aqueous medium. The obtained nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), sedimentation test, scanning electron microscopy (SEM), and X-ray powder diffraction (XRD). Results of FT-IR and TG showed that the desired polymer chains have been covalently bonded to the surface of ZnO nanoparticles. It was found that the increasing monomer concentration could increase the grafting percentage and hence promote the dispersibility. The application of some surfactant is also helpful for dispersion. The viscous properties of nano-suspensions were investigated. The ZnO/PS nanocomposite was prepared by adding PMMA-grafted ZnO into styrene monomer, followed by radical grafting polymerization. The resulted nanocomposite was characterized by TG, DSC (differential scanning calorimetry) and XRD, and the testing results indicated that thermal behaviors of PS were obviously changed.