Advanced oxidation, is the main of research in ozone fields for many years. Ozone generations and uses as an oxidant and also the use of heterogeneous reactor were improve the de development of catalytic ozonation axes. The object of our project is the application of catalytic ozonation for some refractor molecules. Oxalic acid was chosen as a model of refractor molecules. In fact, it is the final product of the degradation by ozone of many organic molecules in aqueous solution. Ozonation have a significant effect on the mineralization of water charged with oxalic acid. In our experiences, the dioxide of manganese and titan and the oxide of cobalt were used as homogenous catalysts. Experiences of ozonation have been done in ambient conditions in a gas-liquid reactor with a capacity of 2 liters. Studies of ozone concentration, type and mass of catalysts and oxalic acid concentration have been done. With 1mmol/l of oxalic acid solution and 43mg/l of ozone, we obtained 50% of maximal oxidation report after 20min. the addition of 1g of MnO2 to the solution in the reactor changed the same report to 85% after 5min. a comparison between MnO2, TiO2 and CoO was done and results prove that the oxide of cobalt is more efficient than the two other catalyst. However, with the same mass added to the reactor 500 mg for each catalyst, the rate of conversion obtained with MnO2 and CoO was nearly 95% and 90% with TiO2 but the kinetic of CoO is faster than the two other catalysts.