In this work, the advanced decomposition of organic dyestuffs used in food and textile industry, such as Malachite Green (MG), was investigated in the presence of a cationic catalyst montmorillonite (P1-PILCs) prepared by ion-exchange method. The obtained material was characterized by BET, FTIR and XRD. The effects of different variables such as: catalyst dose, catalyst/ozone dose, ozonation time and the pH on the mineralization of the synthetic dye were studied and optimal experimental conditions were ascertained. Compared with simple ozonation, the introduction of the catalyst greatly reduces the duration of the process to reach over 95% yield from 110 minutes to some seconds.