The tribological characteristics of PEEK composites fretting against GCr 15 steel were investigated by a SRV-IV oscillating reciprocating ball-on-disk tribometer. In order to clarify the effect of type and size of fillers on the properties of PEEK composites, nano-sized and micro-sized CF and PTFE fillers were added to the PEEK matrix. The thermal conductivity, hardness, and fretting wear properties of PEEK composites reinforced by CF or PTFE were comparatively studied. The results showed that the type and size of the fillers have an important effect on both the friction coefficient and wear rate, by affecting their thermal conductivity, hardness, as well as the surface areas of their transfer films. In comparison, the effect on improving the tribological properties of micro-sized CF was superior to that of nano-sized CF, while the effect of nano-sized PTFE was superior to that of micro-sized PTFE. Considering the acceptable friction coefficient and wear rate of the composite under the fretting wear test, it seemed that 4% nCF, 20% mCF, 2% nPTFE and 10% mPTFE were desired additive proportions. And it also can be found that during the fretting wear test, the abrasive and adhesive wear resulted in accumulative debris at the contacting surface. The transfer films made of debris were formed on the counterfaces.