Abstract: In this study PET was treated by CF4 and CF4/CH4 plasmas. The modified surface was characterized by angle-dependent are and contact angle techniques, It was found that surface modification make the PET surface more hydrophobic. CF4/CH4plasma exhibits stronger effects than CF4 plasma ed alone. Immersing samples in water, the water environment would make the modified surface less hydrophobic as a result of the turnover of the fluorine-containing groups from surface to the bulk.However, CF4/CH4 Plasma could improve the surface stability.