In order to investigate the effect of lanthanum ion implantation on the oxidation behavior of zircaloy at 500℃, Zircaloyspecimens were implanted by lanthanum ions with a dose range from 5×10~(16) to 2×10~(17) ions/cm~2 at room temperature, and then oxi-dized at 500℃ for 100 min. The valence of the oxides in the scale was analyzed by X-ray Photoelectron Spectroscopy (XPS). Thephase structures of the oxides in the scale were examined by Glancing Angle X- ray Diffraction (GAXRD). With the increase of im-planted lanthanum ions dose, the phase structures in the oxide scale are transformed from monoclinic zirconia to hexagonal one andthen to monoclinic one again. The measurement of weight gain showed that a similar change from the decreased gain to increasedone again is achieved in the oxidation behavior of lanthanum ion implanted zircaloy compared with that of as-received zircaloy In order to investigate the effect of lanthanum ion implantation on the oxidation behavior of zircaloy at 500 ° C, Zircaloyspecimens were implanted by lanthanum ions with a dose range from 5 × 10 ~ (16) to 2 × 10 ~ (17) ions / cm ~ 2 at room temperature, and then oxi-dized at 500 ° C for 100 min. The valence of the oxides in the scale was analyzed by X-ray Photoelectron Spectroscopy (XPS). Thephase structures of the oxides in the scale were examined by Glancing Angle X-ray Diffraction (GAXRD). With the increase of im-planted lanthanum ions dose, the phase structures in the oxide scale are transformed from monoclinic zirconia to hexagonal one and then to monoclinic one again. The measurement of weight gain showed that a similar change from the decreased gain to increasedone again is achieved in the oxidation behavior of lanthanum ion implanted zircaloy compared with that of as-received zircaloy