A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and thermodynamics calculation at 673, 773 and 873 K. XRD and SEM analysis indicated that dense and compact oxide films composed of MgO, Y203 and CaO formed. The oxidation behavior was characterized by the selective oxidation. Based on Pilling-Bedworth ra- tio （PBR） and energy dispersive spectrometer （EDS） analysis, Y203 contributed more to form the compact surface oxide film, which led to the excellent ignition-proof performance. The thermodynamics analysis and EDS results implied that the Y-rich areas were preferred paths for the selective oxidation.
