An angle-resolved x-ray photoelectron spectroscopy (XPS) method based on a fiat, uniform, isotropic, and layered model is first introduced for the thickness measurement of ultrathin (< 100 angstrom) double-layer films, such as metal oxide/metal. Since only the relative intensities, at two electron exit angles, of characteristic XPS peaks of metallic species, the material densities and mean free paths of photoelectrons with certain kinetic energy are involved, no dependence of either instrumentation constants or the elemental sensitivities for different species exists in this method and the influence from surface contamination is eliminated intrinsically. The results with error analysis for Al2O3/Al films are reported.