Abstract: Surfacemodified SiO2 particles with γ-metharyloxyethylpropyl trimethoxy silane, a silane coupling agent (KH570), and oleic acid (OA) were insitu synthesized in a solgel process and then were used to prepare polypropylene (PP) composites to enhance their impact toughness. Effects of types of surface modifiers and contents of KH570modified SiO2 particles on tensile, flexural and impact properties, as well as heat resistance and crystallization behavior of the composites were investigated. The results indicated that the modification effect of KH570modified SiO2 particles on PP is better than that of OAmodified ones. The composites achieved the optimum comprehensive properties with the addition of 4 wt % KH570modified SiO2 particles. Their tensile strength kept a stable value in comparison with pure PP, whereas their elastic modulus, flexural strength, flexural modulus and impact strength increased by 46 %, 15 %, 23 % and 14 %, respectively.