An attempt was made to analyze the reaction of carbon with NO or N2O by using an ab initio molecular orbital theory. This method allows the simulation of the chemisorption process of these gas molecules on zigzag and armchair edge sites of carbon. It was found that NO adsorption with the N atom down is more thermally favorable than the adsorption with the O atom down, while the O down mode is more favorable than the N down one for N2O adsorption because the former process releases a stable N-2 molecule to form a surface oxygen complex. The chemisorption of NO or N2O with its bond axis parallel to the edge line gave the most stable chemisorbed species. The presence of surface oxygen complexes (quinone-type carbonyl group) on the edge decreases the strength of some bonds in NO-and N2O-chemisorbed species and consequently lowers their thermal stability. Furthermore, the N-2 formation process in the C-NO/N2O reaction was analyzed and possible N-2 formation routes were proposed. The routes predicted by the molecular orbital theory were compared with the previous experimental results.