Mg-Y-RE alloy is potentially useful in biodegradable implants but the fast degradation rate in the physiological environment restrains actual applications. In order to enhance the corrosion resistance, aluminum and oxygen ion implantation is employed to modify the surface of the Mg-Y-RE alloy. X-ray photoelectron spectroscopy (XPS) is conducted to obtain elemental depth profiles and determine chemical state changes. Electrochemical impedance spectroscopy and potentiodynamic polarization are employed to investigate the electrochemical behavior in simulated body fluids (SBF). After polarization, the corroded surface is further studied by scanning electron microscopy (SEM). The results indicate Al and O ion implantation produces an Al2O3-containing protection layer which improves the corrosion resistance of Mg-Y-RE alloy. After the surface treatment, localized corrosion becomes the dominant corrosion mechanism instead of general corrosion. (C) 2011 Elsevier B.V. All rights reserved.