Abstract: New selenates La₂O₂SeO₄ and Pr₂O₂SeO₄, as well as selenite PbSe⁴⁺O₃ and selenate PbSe⁶⁺O₄, have been studied by X-ray photoelectron spectroscopy (XPS). The elemental and ionic compositions of new selenates containing Se⁶⁺, La³⁺, and Pr³⁺ ions have been confirmed on the basis of XPS parameters of the core and valence electrons. The reduction of Se⁶⁺ ions on the surface of selenite samples to Se⁴⁺ ions under X-ray radiation in the spectrometer chamber has been studied. It has been demonstrated that, unlike the PbSe⁶⁺O₄ selenate, the PbSe⁴⁺O₃ selenite is stable to X-ray radiation. It has been shown that La₂O₂SeO₄ is more stable in air than Pr₂O₂SeO₄.