• PMS activated by ZnO oxygen vacancies was applied for BPA degradation. • One-electron transfer reaction resulting in the formation of OH − and SO 4 − . • Surface-adsorbed radicals play an important role in BPA degradation. • Accurate toxicity of the byproducts was calculated. The activation of peroxymonosulfate (PMS) by multivalent transition metal oxides has been widely studied in organic pollutants degradation. Compared with that of valence electrons, the role of localized electrons of transition metal oxides in the activation of PMS has remained elusive. Herein, ZnO, as a typical irreducible oxide, was used as an ideal model to determine the role of the localized electrons of O-vacancies (V o ) in the PMS heterolysis process. Combined experimental and theoretical analysis demonstrated that O-vacancies, serving as the catalytically active sites, provide enough localized electron retransmission to the adsorbed HSO 5 − , via a single electron transfer reaction resulting in formation of OH − and SO 4 − . In addition, O-vacancies promote PMS dehydration to form metastable − SO 4 -O-O-O 4 S − that rapidly decompose into O 2 − , which is responsible for the 1 O 2 production. This work introduces a unique strategy for obtaining electronic-level insights into the role of catalyst defects in promoting efficient PMS activation.