The catalytic oxidation of aqueous phenol over MnO2/CeO2 mixed oxide catalyst was shown to be accompanied with undesirable formation of heavy polymers on the catalyst surface leading thereby to its deactivation. This deactivation was proved experimentally through comprehensive quantitative and qualitative experimental measurements such as elemental analysis of deactivated catalyst, X-ray photoelectron spectroscopy, and temperature-programmed oxidation coupled with mass spectrometry. Using the Langmuir-Hinshelwood-Hougen-Watson approach, a deactivation-reaction network kinetic model was developed to predict the fate of the Various carbon lumps involved in phenol wet oxidation. It was postulated that deactivation was the resultant of blockage of active sites by fouling species issued from polymerization of parent reactant (phenol) and its daughter intermediate dissolved partially oxidized products. The kinetic model was verified by comparing the experimental results with those foreseen in the simulation for different experimental conditions.