In order to obtain material s with different surface properties, an activated carbon was modified by thermal treatment with 20 % of nitrous oxide in nitro gen at 500°C, for different periods of time, and also with 5% of oxygen in nitrogen at 425°C for 600 minutes and 100% of hydrogen at 950°C for 360 minutes. DRIFTS was used to characterize the surface chemistry of the material treated. The qualitative results show that the treatments with N20 have larger effects on the intensity of the surface groups. These changes could be associated to the incorporation of nitrogen into the carbon matrix. In agreement with literature reports, it could be said that the gas phase oxidation of the activated carbon shows mainly superficial groups such as carboxylic anhydrides, phenols and carboxilates, lactones and quinones