An effective solution mixing method starting from a synthesis solution Of SiO2 nanoparticles was developed for dispersing nanoparticles into high-density polyethylene (HDPE). Spherical SiO2 nanoparticles with narrow size distribution (50-100 nm) were prepared by Stober method, and solvents of the synthesis solution (EtOH/NH4OH) were gradually replaced with toluene by evaporation under reduced pressure. The SiO2 nanodispersion, in toluene and residual ethanol, was mixed and refluxed with dissolved maleic anhydride grafted polyethylene (PEgMA) at a relatively high SiO2 content (17.8 wt %). The PEgMA-SiO2 masterbatch was filtered, dried under vacuum, and mixed with HDPE by melt compounding. SiO2 contents in the final HDPE nanocomposites were 3 and 5 wt %. SEM images of the masterbatch and final composites showed the SiO2 nanoparticles to be well dispersed in HDPE. No agglomerates were observed. FTIR results suggest that the interactions between the maleic anhydride group of PEgMA and hydroxyl groups Of SiO2 surface involve ester and/or hydrogen bonding. Addition of SiO2 particles and PEgMA to HDPE slightly increased Young's modulus, tensile strength, breaking strength, and elongation at break, indicating enhanced toughness of the nanocomposites. The measured Young's moduli of FIDPE-PEgMA-SiO2 composites agreed well with Young's moduli predicted by Mori-Tanaka composite theory. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1218-1225, 2010