Abstract: Objective: To compare the changes of chemical components and contact angles on the surface of PMMA after O2-plasma and Ar-plasma treatment. Methods: 24 test specimens were prepared from an acrylic resin denture material. The specimens were placed in a glass tubular reactor. Imposition of 60W of power created the condition under which plasma treatment was carried out for 2 min. X-ray photoelectron spectroscopy(XPS) studies and contact angle measurements were performed. Results: After O2-plasma and Ar-plasma treatment, the O/C atomic ratios increased from 0.289 to 0.682 and 0.593. Contact angles were reduced from 66.32 °to 41.35 °and 46.16° respectively. Conclusions: Within the limitations of this study, both O2-plasma and Ar-plasma treatment have effect on increasing the amount of oxygen atoms and improving wettability of PMMA. But, the effect of O2-plasma was better than that of Ar-plasma.