Differential scanning calorimetry (DSC) was applied to investigate the isothermal and non-isothermal crystallization behaviors of the nano-silica filled PEEK composites. The inclusion of the 15 nm silica particles would significantly decrease the crystallinity of the PEEK matrix by about 15% under isothermal crystallization. The nano-silica filled PEEK composites show the higher values of Avrami exponent n as compared to those of the neat PEEK at various temperatures, and the n value will increase with increasing silica content. Under non-isothermal crystallization, the crystallization peak temperature of the nano-silica filled PEEK composites will be lowered by 2-4 degrees C as compared with that of the neat PEEK. The crystallinity of the PEEK/SiO2 nanocomposite will exhibit slightly lowered value with increasing nano-silica content, indicating that the inclusion of the nano-silica particles would decrease the mobility of the PEEK molecules. The Avrami exponent n will show a lower value as the cooling rate increases, but exhibit a higher value with increasing nano-silica content, suggesting that the smaller grain size in the PEEK matrix could be resulted in. The combined Avrami and Ozawa equation can well describe the crystallization behavior of the nano-silica filled PEEK composites under non-isothermal crystallization. (C) 2010 Elsevier B.V. All rights reserved.