The engineering of oxygen vacancies in CeO nanoparticles (NPs) allows the specific fine-tuning of their oxidation power, and this can be used to rationally control their activity and selectivity in the photocatalytic oxidation (PCO) of aromatic pollutants. In the current study, a facile strategy for generating exceptionally stable oxygen vacancies in CeO NPs through simple acid (CeO-A) or base (CeO-B) treatment was developed. The selective (or mild) PCO activities of CeO-A and CeO-B in the degradation of a variety of aromatic substrates in water were successfully demonstrated. CeO-B has more oxygen vacancies and exhibits superior photocatalytic performance compared to CeO-A. Control of oxygen vacancies in CeO facilitates the adsorption and reduction of dissolved O due to their high oxygen-storage ability. The oxygen vacancies in CeO-B as active sites for oxygen-mediated reactions act as (i) adsorption and reduction reaction sites for dissolved O, and (ii) photogenerated electron scavenging sites that promote the formation of HO by multi-electron transfer. The oxygen vacancies in CeO-B are particularly stable and can be used repeatedly over 30 h without losing activity. The selective PCOs of organic substrates were studied systematically, revealing that the operating mechanisms for UV-illuminated CeO-B are very different from those for conventional TiO photocatalysts. Thus, the present study provides new insights into the design of defect-engineered metal oxides for the development of novel photocatalysts.