Oxygen-isotopic labelings play important roles in identifying and understanding chemical and biological processes. Direct C=O to C=¹⁸O or C=¹⁷O conversion in a single step leading to labeled compounds can alleviate synthetic burdens without the need for resynthesis. Here we describe a photocatalytic oxygen-isotopic labeling protocol that can efficiently and selectively install ¹⁸O and ¹⁷O on carbonyls of ketones and aldehydes via oxygen isotope exchange with oxygen-isotopic waters (H₂¹⁸O or H₂¹⁷O) as the sources of oxygen isotopes, in which light and oxygen-enabled sodium alkanesulfinates catalyzed this process. This strategy was extended to the in-situ formed ketones from the photocatalytic aerobic oxidation of alkyl arenes and secondary alcohols. Furthermore, reduction of the oxygen-isotopically labeled aldehydes with NaBH₄ provided the corresponding oxygen-isotopically labeled primary alcohols. We believe that the oxygen-isotopically labeling method will be widely used in chemistry, biology and medicine fields.