We report the effect of N2, Ar, and O2 plasma treatments on the surface properties of metals. The carbon atoms reduced more in O2 and Ar plasma than in N2 plasma due to a chemical reaction with O2 plasma and large plasma density in Ar plasma. A water contact angle decreased after the plasma treatment regardless of the kinds of plasma gas, showing the increase in the hydrophilicity in surfaces. Synchrotron radiation photoemission spectroscopy data showed that the work function increased after N2, Ar, and O2 plasma treatments in sequence. This is due to the reduction of carbon atoms and the formation of O-rich surface in O2 plasma case.