<p>The investigation presented herein reveals a new Fenton-type catalytic system of ammonium phosphomolybdate (APM) in conjunction with hydrogen peroxide (H₂O₂) in ambient conditions to facilitate the degradation of sulfonamide drug sulfamethoxazole (SMX). Delving into the intricate mechanisms underlying SMX degradation within the APM/H₂O₂ system constituted the core of this study. It is revealed that in the APM/H₂O₂ system, a catalytic redox mechanism involving Mo(VI) and Mo(V) state interconversion occurs in the presence of H₂O₂ producing superoxide (^•O₂⁻) and hydroxyl (^•OH) radicals, which degrade the SMX molecule in a stepwise fashion. Operating at a temperature of 30&#xa0;°C, the efficacy measurements reveal an impressive removal rate of 98.3% for SMX alongside 86.4% for total organic carbon (TOC). Furthermore, the identification and analysis of transformation products (TPs) unravel the potential pathways governing the catalytic decomposition of SMX. The mineralization of SMX involves the cleavage of the oxazole ring, disruption of the S-N bond, and Smiles-type rearrangement, thereby engendering the production of minor organic acids, including maleic, oxalic, oxamic, and pyruvic acid. These intermediate species subsequently undergo mineralization. The APM/H₂O₂ system is further explored to efficiently degrade SMX in real wastewater. As far we know from literature review, this will be the first reported study of antibiotic degradation using the APM/H₂O₂ system to show excellent efficiency in normal and real wastewater systems.</p>