Organosulfates (OSs) are ubiquitously present in atmospheric aerosols and cloud droplets, and affect aerosol-cloud-climate interactions via their distinct physicochemical properties. Although various formation pathways and transformation mechanisms have been proposed, the origins of many atmospheric OSs remain unclear or unexplained. In this study, we investigated the aqueous-phase oxidation of an <em>α</em>-pinene-derived organosulfate (C<sub>10</sub>H<sub>17</sub>O<sub>5</sub>SNa, <em>α</em><span>pOS-249</span>) by <sup>•</sup><span>OH</span> radicals as a potential source of some uncharacterized atmospheric OSs by quantifying the kinetics and characterizing the reaction products. An aqueous-phase photoreactor was used to conduct the aqueous-phase <sup>•</sup>OH oxidation of<em> α</em>pOS-249, revealing a rate constant of (2.2 ± 0.2) × 10<sup>9</sup> L mol<sup>–1</sup> s<sup>–1</sup> and atmospheric lifetimes ranged from minutes to about 2 days under atmospherically relevant cloud conditions. The product analysis revealed that a variety of more oxygenated C<sub>10</sub> OS products, smaller OS (<C<sub>10</sub>) products, and inorganic sulfates (e.g., bisulfate and sulfate) can be produced via functionalization and fragmentation processes upon oxidation. Most of the OS products have been detected in the atmosphere, with some of them whose sources and formation mechanisms are unknown thus far. Our study provides a new perspective that the chemical transformation of larger OSs via aqueous-phase oxidation can proceed efficiently to yield a variety of new OSs, serving as a source for atmospheric OSs, particularly smaller OSs. These findings would be useful in field data interpretation and model simulations regarding the abundance, formation, transformation, and atmospheric fates of OSs.