The intensification of the degradation of antipyrine in aqueous solution by using a UV-A-LED-photo-Fenton reaction intensified by ferrioxalate complexes and with addition of persulfate anions was studied. The efficiency of the reaction was evaluated in terms of antipyrine degradation and mineralization degree at different initial concentrations of hydrogen peroxide, ferrous ion, oxalic acid and persulfate anion. The reaction was carried out using a lab-scale photoreactor irradiated with artificial UV-A-LED light emitting at 365 nm. Artificial neural networks (NNs) were implemented for modelling the degradation process. Under optimal conditions, complete degradation of antipyrine and 93% mineralization was reached in 2.5 and 60 min, respectively. The contribution of HO radicals in this system was evaluated running the reaction in the absence and presence of appropriate quenchers such as tert-butyl alcohol and methanol. In the last step of reaction, possibly different intermediates such as 2-butenedioic acid, butanedioic acid, 4-oxo-pentanoic acid, acetate and formate can be generated which cannot be degraded by HO radicals or their reaction is very slow. This ferrioxalate-mediated system reduces the amount of H2O2 needed (100 mg L−1) for antipyrine degradation and persulfate was not necessary because it could not be activated with UV-A LED nor with Fe2+ since it is quickly converted to Fe3+ forming ferrioxalate complexes.