Argon gas was bubbled during plasma electrolytic oxidation (PEO) treatment of magnesium alloy in a silicate solution. The appearance of arcs and plasma discharging was locally concentrated on the magnesium alloy surface and phase fraction of Mg2SiO4 in the oxide layer was increased due to Argon gas bubbling. The higher energy density of the Ar plasma atmosphere is believed to contribute to the effective formation of the high temperature phase (Mg2SiO4), particularly in the inner layer. Furthermore, the PEO treated Mg alloy with Ar bubbling showed improved corrosion resistance by a change of open pores structure. (C) 2012 Elsevier B. V. All rights reserved.