The fretting wear behaviors of perfluorinated ethylene-propylene copolymer (FEP) were studied on an SRV fretting wear tester with the plane contact of FEP against a bearing steel at room temperature of about 15ะC. In our tests, the product of load (L) and total sliding distance (S) was preset to be a constant as the wear coefficient K v can be expressed as K v ร
WrP m /(LrS), where W is the volume of material loss, P m is the flow pressure of the softer material (FEP), L and S are the load and the total sliding distance, respectively. Under our test conditions, no wear of the bearing steel was observed when fretted against FEP. The sudden change of wear rate of FEP or its wear weight was governed by the critical PV value, an important parameter for polymers and polymer composites under sliding friction, which was the product of normal stress and average sliding speed. The critical PV value of FEP under study was 3 1 10 4 Parm/s. It was also found that the topography of wear trace formed on FEP were fairly well corresponding with that of their transferred films on steel surface. Both on worn surface of FEP and on metal surface, three sharply defined regions, wear debris formation region, high-stress region, and slightly sliding wear region, can be distinguished. It indicated that the higher the normal stress, the more difficult the formation of thick transfer film.