Abstract: The inter facial structure of Ti/single-cry stal Al₂O₃( 0001), Ti/poly crystalline Al₂O₃, and Ti/single-crystal MgO( 001) system made by RF magnetron sputtering was investigated by using XPS combining with Ar⁺ ion insituetching in this paper. The results show that the reduction of Al³⁺ and oxidation of tit aniumexist at the interface of Ti/Al₂O₃ systems. Moreover, the reduced Alappears before the oxided Tiat the interface of Ti/Al₂O₃ in the etching process. Nosimilar interfacial reaction was observed at the interface of Ti/MgO system by the same making method.