Abstract <p>Constructing highly efficient and durable water electrolysis cell system is of crucial importance to meet the requirements of renewable hydrogen energy conversion strategy. However, the underdevelopment of water oxidation half-reaction is well-known to greatly hinder the practical hydrogen production. Although there have been numerous efforts in the design of oxygen evolution reaction (OER) electrocatalysts, the roles of electrolytes in OER activity are less systematically studied. In this review, the pivotal roles pH, cations, anions and salt ions within electrolyte in altering the intrinsic mechanism of OER have been especially discussed, respectively, based on some recent advances in understanding electrolyte effects on OER. Therefore, we highlight the importance of electrolyte compositions in affecting (de)protonation, catalyst structure evolution, reaction intermediates, water structure/network and stability. These insights could profoundly reveal how the electrolyte engineering determines catalytic performance, modulates catalytic active sites and alters change transfer mechanisms at the electrode interface. Such understandings could pave the way for the rational design of highly efficient electrocatalytic OER, CO₂ reduction and N₂ reduction systems. Finally, we discuss the challenges and future perspectives of electrolyte effects on OER, the intrinsic charge transfer mechanisms in electrocatalysis systems and the potential applications of electrolyte engineering in industrial settings.</p> Graphical Abstract <p></p>