Ta/MgO x /Ni 81 Fe 19 /MgO x /Ta films were prepared by magnetron sputtering. The anisotropic magnetoresistance (AMR) increases dramatically after annealing. The chemical states of Ta and MgO x at the interface of the NiFe/MgO x /Ta films, which were prepared at the different technological conditions, were analyzed by X-ray photoelectron spectroscopy (XPS). The results show that the AMR of the films is related to the chemical states of MgO x . The chemical states of Mg are different when MgO x is prepared at different technological conditions. Therefore, increasing the AMR is beneficial when more Mg 2+ ions are present in the MgO x films.