<p>This study investigated the degradation effects and mechanisms of methylene blue (MB) utilizing an ultraviolet-activated permanganate (UV/KMnO₄) system under various operational parameters. The UV/KMnO₄ system achieved 66.3% MB degradation within 5 min, a process predominantly driven by hydroxyl radicals (•OH) and reactive manganese species (RMnS). It was determined that the degradation efficiency could be enhanced by optimizing the KMnO₄ dosage, reducing the initial MB concentration, and elevating the reaction temperature. The reduction in pH not only promoted the generation of reactive species but also enhanced the catalytic activity of KMnO₄ and the dissociation of MB, culminating in a degradation efficacy of 98.6% at pH 4.0. The presence of Ca²⁺ and Mg²⁺ was found to reduce degradation efficiency via flocculation effects. Conversely, humic acid (HA) impeded the degradation by competing for reactive species and a robust light-filtering properties. The introduction of CO₃²⁻/HCO₃⁻ resulted in the quenching of •OH, thereby decreasing the degradation of MB. In contrast, the addition of NO₃⁻ facilitated the generation of both •OH and reactive nitrogen species, which accelerated the degradation rate by 18.1%. The presence of Cl⁻ and SO₄²⁻ showed negligible influence on MB degradation. The inference of the degradation pathway revealed that MB was transformed into 20 distinct oxidation byproducts through demethylation, hydroxylation, and polymerization reactions, raising concerns regarding the potential toxicity of these transformation products. In summary, this study elucidated the degradation kinetics and mechanisms of MB within the UV/KMnO₄ system and expanded the boundaries of KMnO₄ pre-oxidation for the elimination of organic pollutants.</p> Graphical Abstract <p></p>