This paper deals with the modifications of the chemical surface functionalities and the textural changes of a glassy carbon produced by three oxidizing agents: ozone, hydrogen peroxide, and oxygen plasma. The chemical surface changes are evaluated by using Fourier transform infrared spectroscopy, temperature programmed desorption-mass spectrometry, and chemical titrations of the surface functionalities by using the Boehm method. The textural modifications are studied by mercury porosimetry and by N-2 and CO2 adsorption at 77 and 273 K, respectively. Ozone is a more effective oxidizing agent than H2O2 and oxygen plasma. It is able to introduce much larger amounts of oxygen functionalities on the surface than the other oxidizing agents. Moreover, the textural characteristics of the original sample remain almost unchanged after the treatments with oxygen peroxide and with oxygen plasma, while ozone produces modifications in surface area and mesoporosity. Nevertheless, ozone modifications of surface area seem to be partially produced by the fixation of the oxygen functionalities at the entrance of the micropores which partially hinder the access of the adsorbates.