The aim of this study is to prepare a good dispersion and distribution of nanosilica particles in poly (ether ether ketone), (PEEK), matrix by using a high energy ball milling technique. First, the surface of silica nanoparticles was modified with a silane coupling agent (3-glycidoxypropyltrimethoxysilane). Then the mixture of PEEK powder and surface modified silica nanoparticles was subjected to ball milling at ambient temperature for 15 h under argon atmosphere. Morphology, particle size distribution and crystalline structure of PEEK/SiO2 during milling were characterized by scanning electron microscope (SEM), laser diffraction particle size analyzer and X-ray diffraction (XRD) techniques. The effect of surface pretreatment of silica nanoparticles on dispersion in the matrix was evaluated by means of transmission electron microscope (TEM). The results indicated that after ball milling for 15 h, SiO2 nanoparticles were well deagglomerated and dispersed homogeneously in PEEK matrix. TEM results confirmed that the dispersion of modified silica nanoparticles in PEEK matrix is more uniform than unmodified ones. Differential scanning calorimetry (DSC) data revealed that both milling process and presence of silica nanoparticles affect on the melting temperature and crystallization behavior of PEEK. It was also shown that milling results in a decreasing PEEK crystallinity. (C) 2010 Elsevier B.V. All rights reserved.