Abstract: The PA66-based nano-composites containing nano-SiO₂ were prepared in a twin-screw extruder by melt compounding，and the mechanical and thermal properties of the nano-composites were investigated. The results of mechanical testing show that the tensile strength and Young's modulus of the nano-composites are all reinforced with the addition of silica nano-particles. The tensile strength reaches a maximum at 3% mass fraction，which is 11.2% higher than that of the pure PA66. And the Young's modulus reaches a maximum at 5% mass fraction，which is 30.1% higher than that of the pure PA66. The storage modulus and glass transition temperature of the composites obviously increase compared with those of the pure PA66. The differential scanning calorimetry (DSC) indicates that the incorporation of nano-SiO₂，on the one hand，can hinder the crystallization process of PA66. On the other hand，it can act as a nucleation agent and increase the nucleation site and nucleation rate of PA66.