The influence of ball-milling in the texture and surface chemistry of multi-walled carbon nanotubes (MWCNT) was studied in this work. Treatment times up to 360 min at constant frequency (15 vibrations/s) and frequencies from 10 to 20 vibrations/s during 30 min were used for the preparation of the modified samples. These were characterized by nitrogen adsorption at -196 degrees C, temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The milled samples were used as catalysts for the ozonation of oxalic acid. The surface area of the MWCNT increases, whereas the particle size decreases with the ball-milling time until 240 min at 15 vibrations/s. The functionalization of MWCNT surface is not achieved by ball-milling under the conditions used. The catalytic performance of the ball-milled samples for oxalic acid mineralization increased significantly when compared to the unmilled MWCNT. Therefore, ball-milling is an effective and simple method to increase the surface area of commercial carbon nanotubes without significant changes of their structural properties, and, consequently, this method allows increasing their catalytic performance in ozonation processes. (C) 2014 Elsevier B.V. All rights reserved.