Persulfate (PS) activation reaction,which forms sulfate radical (SO4•−), can be used to degrade organic pollutants in water. However, a drawback of this reaction is that the regeneration of ferrous ions requires a high concentration of hydrogen peroxide (Fenton-like reaction) or use of UV radiation. Catechin (CAT), a non-toxic antioxidant of natural origin from tea, is used in this work to improve the sulfate radical-mediated degradation of atenolol (ATL, a model pollutant) in water using relatively low concentrations of reactive chemical species (less than 100 μM). To the best of the author's knowledge, the direct effect of CAT on the oxidation state of iron,which is promoted by the reduction of ferric into ferrous ions with the enhancement of SO4•− formation in the presence of PS, is demonstrated for the first time. The enhancement versus inhibition effect of CAT and the chemicalmechanismof the iron-based activation process are explained. Results show that UVA radiation, which is representative of solar light, accelerates the initial degradation of ATL bymore than 30% through ferric iron photolysis. Finally, a reaction mechanism leading to the formation of hydroxyl radicals (HO•) and SO4•− is proposed considering the implication of different activation/reaction chemical steps.