Nitrogen-doped carbon xerogels were tested as metal-free catalysts for the mineralization of oxalic acid by ozonation and by wet air oxidation. Oxalic acid was completely mineralized in less than 45 min in wet air oxidation, but complete conversion was never achieved with ozone. Some general trends were observed, and correlations between the catalytic activity and the surface chemistry of the carbon materials were established. In particular, the apparent reaction rate constants for both processes correlate with the concentration of surface nitrogen. The effect of N-doping is particularly effective in CWAO, the rate constants increasing by two orders of magnitude in comparison with the nitrogen-free material. With ozone, oxidation of oxalic acid may occur both in the liquid phase (homogeneous reaction) and on the catalyst surface, while wet air oxidation appears to proceed mainly on the carbon surface.