Oxidative desulfurization routes appear among the most promising methods for obtaining ultralow-sulfur diesel fuels requested worldwide by environmental legislation, in this work, the oxidation kinetic of benzo- and dibenzothiophene with the oxidizing system constituted by hydrogen peroxide and formic acid was studied in isothermal conditions at 40 degrees C. Since the oxidation occurs in a heterophasic system, both physical and chemical phenomena play an important rule. The aim of this work was to interpret the obtained experimental conversions with a model able to capture the influence of both mass transfer and chemical kinetics. The results allowed verification that the oxidation reaction occurs in the slow liquid liquid reaction regime and chemical kinetics is the controlling step. The identified values of the intrinsic kinetic constants for the oxidation of benzo- and dibenzothiophene are 2.255 x 10(-1) and 1.206 x 10(0) m(3) kmol(-1) s(-1), respectively.