In this study, metal-free electrocatalysts were obtained from the pyrolysis of commercial Kevlar (TM) and Twaron (TM) carbon fibers (pKf and pTf, respectively). An easy and low cost synthesis method was developed. The obtained electrocatalysts have a significantly lower cost than conventional platinum based electrocatalysts. Synthesis of the electrocatalyst was made by pyrolysis treatment of the carbon fibers, under nitrogen atmosphere, followed by an activation treatment under carbon dioxide atmosphere. Properties and electrochemical performance of pyrolyzed (pKf, pTf) and activated (aKf and aTf) samples were compared. The electrocatalysts obtained have surface areas of up to 1000 m(2)/g after the activation treatment. Morphology and structural characteristics were studied by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS). The electroactivity of these electrocatalysts was evaluated by the oxygen reduction reaction (ORR) in acid media by rotating disk electrode technique. Carbon fibers showed an improvement in the ORR after receiving the activation treatment. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.