The oxidation state of Fe and Ti ions implanted in yttria stabilized zirconia (YSZ) was studied by XPS (X-ray photoelectron spectroscopy) in combination with depth profiling using Ar+ sputtering. In the “as-implanted” state of the sample Fe was found to be present as Fe3+, Fe2+ and as metallic Fe0. This is in agreement with earlier conversion electron Mössbauer Spectroscopy measurements. For Ti-implanted YSZ in the “as-implanted” state the majority of the Ti is present as Ti4+, Ti3+, and Ti2+ ions, while a part of the Zr cations is present in the divalent oxidation state (Zr2+). After oxidation in air, the Fe and Ti ions are present only in the valence three and four oxidation states, respectively.