Surface properties of polycarbonate (PC), polypropylene (PP), polyethylene terephthalate (PET) samples treated by microwave- induced argon plasma have been studied with contact angle measurement, X-ray photoelectron spectroscopy (XPS) and scanned electron microscopy (SEM). It is found that plasma treatment modified the surfaces both in composition and roughness. Modification of composition makes polymer surfaces tend to be highly hydrophilic, which mainly depended on the increase of ratio of oxygen-containing group as same as other papers reported. And this experiment further revealed that C=O bond is the key factor to the improvement of the hydrophilicity of polymer Surfaces. Our SEM observation Oil PET shown that the roughness of the surface has also been improved in micron scale and it has influence on the surface hydrophilicity. (c) 2005 Elsevier B.V. All rights reserved.