Zorflex® activated carbon fibers (ACF), reference FM100 198B, are used beforeand after an oxidizing procedure with H 3 PO 4 to study the adsorption of Pb 2+ . The point ofzero charge was determined for the modified and unmodified fiber giving values of 2.3 and4.3, respectively. After oxidizing the ACF, the fiber showed to have a greater Pb 2+ adsorptioncapacity in comparison with the unmodified fiber, which is related with the acid sites increase,where lead was mainly adsorbed. Determination of the BET area was carried out by nitrogenphysisorption at 77K. ACFs presented superficial areas between 1000 and 1500 m 2 /g showingmostly, a microporous structure. The preliminary design of an adsorbent using the modifiedfiber is presented where the fiber superior physicochemical properties over the unmodifiedone are observed.