AbstractOxygen vacancies are usually thought to be beneficial for photogenerated charge separation. In this work, the oxygen vacancies in ov‐Bi2O3 (Bi2O3 with oxygen vacancy) were found to be able to produce 1O2 in the dark owing to chemical adsorption. The oxygen vacancies were further found to be responsible for ov‐Bi2O3 exhibiting higher 1O2 generation under light irradiation with 1O2 as the only reactive oxygen species (ROS) than Bi2O3 with 1O2, H2O2, and others as the ROS. The photocatalytic activity was investigated for the selective photo‐oxidation of phenyl methyl sulfide to phenyl methyl sulfoxide and phenyl alcohol to benzaldehyde. In either case, ov‐Bi2O3 displayed better performance than Bi2O3, suggesting the significant role of oxygen vacancies in modulating the photocatalytic oxidation properties. This work provides an alternative approach to obtain singlet oxygen, which may guide further design of photocatalysts with high efficiency and selectivity towards photocatalytic organic synthesis.