AbstractThe proherbicide Isoxaflutole (IXF) hydrolyzes spontaneously to diketonitrile (DKN) a phytotoxic compound with herbicidal activity. In this work, the sensitized degradation of IXF using Riboflavin (Rf), a typical environmentally friendly sensitizer, Fenton and photo‐Fenton processes has been studied. The results indicate that only the photo‐Fenton process produces a significant degradation of the IXF. Photolysis experiments of IXF sensitized by Riboflavin is not a meaningful process, IXF quenches the Rf excited triplet (3Rf*) state with a quenching rate constant of 1.5 · 107 m−1 s−1 and no reaction is observed with the species O2(1Δg) or generated from 3Rf*. The Fenton reaction produces no changes in the IXF concentration. While the photo‐Fenton process of the IXF, under typical conditions, it produces a degradation of 99% and a mineralization to CO2 and H2O of 88%. A rate constant value of 1.0 × 109 m−1 s−1 was determined for the reaction between IXF and HO˙. The photo‐Fenton process degradation products were identified by UHPLC‐MS/MS analysis.