Abstract: The effects of polytetrafluoroethylene (PTFE) -based composites filled with nanosized SiO₂ and micronsized SiO₂ on friction and wear properties were investigated. The friction coefficient, wear rate and crystallinity were measured. The friction surface was observed by scanning electron microscopy (SEM). The results show that the addition of the silica micron-particles or nano-particles and surface treatment not only increases the friction coefficient of PTFE-based composites, but also results in largely decreasing the wear rate of SiO₂/PTFE composites. When the filler mass fraction is lower than 6%, the wear rate of the SiO₂/PTFE composites filled with untreated nanosized SiO₂ falls 98.5%, while the wear rate trends to be stable after the filler mass fraction is higher than 6%. However, adding 6% of nanosized SiO₂, the friction coefficient of SiO₂/PTFE composites is only elevated from 0.1 of the pure PTFE to 0.12. The friction coefficient of SiO₂/PTFE composites filled with nanosized SiO₂ treated by coupling agent is improved to the smallest elevation.