In this paper, the phenol mineralization by Ce3+-doped CeO2 by photocatalysis at room temperature, is shown for the first time. The photocatalytic behavior of CeO2 was improved through the incorporation of Ce3+ into its crystalline lattice. The materials were prepared by the precipitation method at low temperatures varying the Ce4+:Ce3+ molar ratio of the precursors during the synthesis process. It is worth noting that, the synthesized photocatalysts did not carry out a thermal treatment after their preparation. The results obtained from Raman analysis demonstrated the formation of oxygen vacancies by the incorporation of Ce3+. The improvement of the photocatalytic activity was attributed to an optimal content of Ce3+ which promoted structural defects (such as oxygen vacancies). Radical species, such as O2.−, are mainly formed during the photocatalytic process, which are probably the main responsible for inducing the mineralization process of the studied pollutant.