Seawater electrolysis has attracted considerable attention in hydrogen production. However, the chloride ions (Cl⁻) in seawater can corrode metal sites and decrease the lifespans of the oxygen evolution reaction (OER). Herein, we report a reversed-active sites strategy, converting Cl⁻-affinitive metal sites to Cl⁻-repellent oxygen sites, for OER in alkaline seawater electrolysis. First, ex/in situ experiments confirm the effectiveness of such a strategy using typical perovskites following the adsorbate evolution mechanism (AEM) or lattice oxygen-mediated mechanism (LOM). Furthermore, the origins of the superior activity and durability of as-prepared La_0.3SrCo_0.5Fe_0.5O_x (La0.3) can be ascribed to higher participation of lattice oxygen in OER, rapid bulk oxygen diffusion, and excellent OH⁻ adsorption kinetics. Hence, an alkaline seawater electrolytic cell with La0.3 as the anode produces 10 mA cm⁻² at just 1.57 V and maintains near-constant activity over 150 hours. This work introduces novel concepts for the production of superactive and steady electrocatalysts for the electrolysis of seawater.