Ferrate( vi ), FeO 4 2− , is a very powerful oxidant that can oxidize a wide variety of inorganic and organic compounds. However, the mechanisms of many of these oxidation reactions have not been studied in detail. In this work, we have investigated the kinetics and mechanism of the oxidation of 4-alkylbenzenesulfonates by ferrate in aqueous solutions at pH 7.45-9.63 by UV/Vis spectrophotometry. The reactions are first order with respect to both ferrate and 4-alkylbenzenesulfonate. The second-order rate constants for the oxidation of 4-isopropylbenzenesulfonate by ferrate at 25 °C and I = 0.3 M are found to be (5.86 ± 0.08) × 10 −1 M −1 s −1 and (4.11 ± 1.50) × 10 −3 M −1 s −1 for Fe(O) 3 (OH) − and FeO 4 2− , respectively, indicating that Fe(O) 3 (OH) − is two orders of magnitude more reactive than FeO 4 2− and is the predominant oxidant in neutral and slightly alkaline solutions. This is further supported by the effect of the ionic strength on the rate constant. No solvent kinetic isotope effect (KIE) was found but a moderate primary KIE = 1.6 ± 0.1 was observed in the oxidation of 4-ethylbenzenesulfonate and 4-ethylbenzenesulfonate-d 9 . Alkyl radicals were trapped by CBrCl 3 in the oxidation of alkylarenes by ferrate. Combined with DFT calculations, a hydrogen atom transfer (HAT) mechanism was proposed for the reactions between Fe(O) 3 (OH) − and 4-alkylbenzenesulfonates. Based on the kinetic study and DFT calculations, the mechanism of the oxidation of alkylbenzenesulfonates by ferrate(VI) in aqueous solutions is found to be hydrogen atom transfer (HAT).