Catalytic wet air oxidation reaction (CWAO) of stearic acid is carried out in a batch reactor over a series of transition metal-based perovskite samples synthesized by reactive grinding. It is observed that the LaCoO3 sample presents the highest initial activity for this reaction. For comparison, pure and substituted LaMnO3 samples show largely smaller activity in spite of similar specific surface areas. The results show that the accessibility of the low temperature active oxygen (or the reducibility of the transition metal) on the surface of the catalyst conditioned the initial activity of the catalyst. Then, a mechanism involving the reaction of stearic acid molecules with adsorbed oxygen surface site (CO3+O2-) is proposed on the basis of the experimental results. Stearic acid oxidation proceeds via a recurrent decarboxylation process that results in the reduction of cobalt surface sites and formation of surface carbonate species (CO3-). In opposition to what was observed for gas phase oxidation reactions, lanthanum (and Ce or Sr) is found to be massively carbonated during the reaction, leading to the destruction of the perovskite structure and loss of the catalytic activity. (C) 2007 Elsevier B.V. All rights reserved.