The influence of 6 keV Ar+ ion bombardment on the LaPO4 surface composition has been studied by XPS. LaPO4 is a material which is particularly attractive as a possible host for high-level radioactive wastes. It was shown that the composition of the altered layer can be described by the mechanism of post-collisional interaction of ion-induced decomposed species and can be presented as: LaPO4 → μ1LaPO4 + μ2LaPxOy + μ3La2O3, where n1 = concentrations of different components. We also received that O1s line synthesis gave the ratio of LaPO4 and La2O3 is 3.5.