The reaction between Fe2+ and HClO constitutes a promising advanced oxidation process (AOP) for removing pollutants from wastewater, and (OH)-O-center dot has been considered the dominant reactive oxidant despite limited evidence for this. Herein, we demonstrate that the Fe2+/HClO reaction enables the production of (FeO2+)-O-IV rather than (OH)-O-center dot in acid medium, a finding that is strongly supported by multiple lines of evidence. Both X-ray absorption near-edge structure spectroscopic tests and Mossbauer spectroscopic tests confirmed the appearance of (FeO2+)-O-IV as the reactive intermediate in the reaction between Fe2+ and HClO. The determination of (FeO2+)-O-IV generation was also derived from the methyl phenyl sulfoxide (PMSO)-based probe experiments with respect to the formation of PMSO2 without (OH)-O-center dot adducts and the density functional theory studies according to the lower energy barrier for producing (FeO2+)-O-IV compared with (OH)-O-center dot. A dual-anode electrolytic system was established for the in situ generation of Fe2+ and HClO that allows the production of (FeO2+)-O-IV. The system exhibits an enhanced capacity for oxidizing a model pollutant ( e.g., phosphite) from industrial wastewater, making it an attractive and promising AOP for the abatement of aqueous contaminants.