The depth profiling of the interface of Ta 2O 5Ta has been investigated and a new model to explain the profile data based on the altered layer induced by bombardment with energetic ions during the profiling has been proposed successfully. The experimental data can be fitted very well and the parameters characteristic of the ion-mixing and pile-up effects can also be obtained by this model. The sample was prepared by the method of anodic oxidation with a thickness of 500 Å. All the surface analyses were performed by scanning Auger microprobe, model PHI-590 at room temperature. The following results have been obtained: the depth profile curve does not follow the form of an error function; the dominant factor for Auger signal during the interface analysis is the altered layer with the thickness of 30–50 Å, rather than the electron mean free path (MFP); and the depth profiling resolution of interface analysis is determined by compromise between the ion-mixing and pile-up effects.