Graphical abstract: An activated carbon fiber was oxidized with ammonium persulfate solutions (APS) and used for the adsorption of Pb(II) from aqueous solutions. A comprehensive study on the effect of the oxidation process conditions - oxidant concentration, oxidation temperature and time - on the obtained fibers Pb(II) adsorption capacity and their chemical and physical properties was done. Samples were characterized by elemental analysis, Boehm titration, N2 adsorption-desorption isotherms and infrared spectroscopy. Adsorption isotherms were obtained for the activated carbon fibers and for two commercial ion-exchange resins, and they showed good agreement with the Langmuir model. For the first time, an activated carbon fiber with a high adsorption capacity for aqueous Pb(II) was obtained (2.70mmolg−1, ca. 559mgg−1). This value was more than 10 times higher than that of the pristine fiber and superior to those of the commercial ion-exchange resins. The adsorption kinetics data of the oxidized activated carbon fiber were studied by different kinetic models and found to be better described by the pseudo-second order model, while the adsorption equilibrium could be reached in less than 2h. It was confirmed that the adsorption process mainly occurred by an ion-exchange mechanism. The obtained results showed that APS oxidation is capable of producing activated carbon fibers with high adsorption capacities for aqueous Pb(II), making them promising materials for industrial wastewater treatment applications.