Advanced oxidation processes (AOPs) are widely proposed for treating persistent pollutants by the ^⋅OH radicals generated from H₂O₂ decomposition. However, their broad applications in practical settings have been hampered by the low efficiency of H₂O₂ decomposition. Here, we report that metal sulfides (MoS₂, WS₂, Cr₂S₃, CoS₂, PbS, or ZnS) can serve as excellent co-catalysts to greatly increase the efficiency of H₂O₂ decomposition and significantly decrease the required dosage of H₂O₂ and Fe²⁺ in AOPs. Unsaturated S atoms on the surface of metal sulfides can capture protons to form H₂S and expose metallic active sites with reductive properties to accelerate the rate-limiting step of Fe³⁺/Fe²⁺ conversion. The efficiency of AOPs involving co-catalysts can be further enhanced by visible-light illumination thanks to the sensitization of organic pollutants. This discovery is expected to drive great advances in the use of AOPs for large-scale practical applications such as environmental remediation.