Abstract: The PA66-based composites containing surface modified nano-SiO₂ with different treatments were prepared in a twin-screw extruder by melt compounding. The interaction of different surface modified nano-SiO₂ and PA66 in composites systems was studied by FTIR and XPS, and the thermal properties of composites were investigated. The results show that different surface modification treatments bring different interface interactions between nano-SiO₂ and PA66, which can influence the melting and crystallization behavior of the PA66 matrix. The presence of modified nano-SiO₂ can result in a lower crystallization temperature and smaller grain size of composites compared with pure PA66 and cause changes in crystallinity of nano-SiO₂/PA66 composites. The TGA and DMA results indicate that surface modification structures of nano-SiO₂ can produce effect on the thermal stability and glass transition temperature of nano-SiO₂/PA66 composites.