Abstract: The waste fly ash obtained from coal-fired power plants was refined by physical ball milling, activated with a silane coupling agent, and then used as a filler to prepare polypropylene (PP) matrix composites by melt blending. The results indicated that, compared to pure PP, the composites exhibited an increase in bending strength by 11.5 %, in tensile strength by 10.7 %, and in impact strength by 34.1 % when using the fly ash only treated by ball milling. Moreover, there was an improvement in the melt flow index and thermal stability of the composites. When the fly ash was treated with a silane coupling agent and then used for PP, the resulting composites showed a further improvement in mechanical properties and thermal stability. Based on our experimental results, there was a good toughening effect on PP when 20 wt% of surface-modified fly ash was incorporated, thus leading to optimal comprehensive performance for PP composites.