Olive oil mill wastewater (OOMW) - the liquid waste generated in the process of olive oil extraction contains significant amounts of phenolics. Their high polluting charges that are measured in BOD5 and COD levels up to 35 g dm(-3) and the presence in the concentrations up to 10 g dm(-3) are of special concern to the environment. These compounds make OOMW biorefractory in nature and unsusceptible to a conventional biological treatment. Reducing their toxicity prior to the conventional treatment is therefore of the uttermost importance. The non-selective catalytic wet peroxide oxidation (CWPO) process is one of the methods that can be used for that purpose in practice. With the use of catalysis the process can be successfully operated under mild conditions with low energy consumption. In this work, the influence of the reaction parameters and the catalyst preparation method on the activity and stability of zeolite (13X) based catalyst in the reaction of hydrogen peroxide oxidation of phenolic compounds present in wastewater from industry for processing olives and olive oil was examined. The reaction was carried out in a batch reactor at different stirring speed, particle sizes, temperatures, catalyst loadings and initial concentrations of hydrogen peroxide. The catalyst Cu/13X was prepared by ion exchange of commercial 13X zeolite. Characterization of the catalyst included N-2 physisorption, XRD, TPD-CO2 and FTIR-Pyridine desorption. In order to increase the catalyst's stability, it was subjected to a thermal post-synthesis treatment at 1273 K. The justification for post synthesis treatment of the catalyst is reflected in the enhanced stability of the catalytically active material which is removed from the carrier, i.e. larger resistance of Cu/13X - K1273 to leaching. Examining the effect of the mixing rates and catalyst particle sizes on reaction rate it was found that the reaction is carried out in the kinetic regime, with the total phenols content diminished by more than 80 % with a 20 % decrease in wastewater's TOC content and leaching below 3 wt. %.