In the present study, 8YSZ:Eu3+ powder was synthesized using co-precipitation route. The evolution of phase composition and fluorescence properties of 8YSZ:Eu3+ powder have been assessed after being subjected to hydrothermal degradation for different times. Morphology and microstructure of the sintered powder were observed by transmission electron microscope (TEM) and scanning electron microscope (SEM). XRD, Raman spectra, photoluminescence (PL) spectra and the decay curve were used to evaluate the phase composition variation and fluorescence properties variation of the powder. The results showed that 8YSZ:Eu3+ powder had a pure tetragonal phase structure. Under hydrothermal degradation conditions, due to the reaction of OH− and oxygen vacancy, the transformation of tetragonal to monoclinic occurred, furthermore the fluorescence properties of the powder were altered.