AbstractIn water treatment process ozone is applied to disinfection and to remove organic pollutants. Membrane contactor devices are used as a physical barrier to separate two fluids without phase dispersion and it can be used to improve the ozonation efficiency. Polymeric materials are used in membrane contactors and they can react with ozone, suffering degradation and losing its mechanical properties. In this work, commercial polymeric membranes were selected to investigate their interaction with ozone in gaseous phase. It was evaluated changes in polymer structures and in membrane morphology by FTIR, DSC, TGA and SEM. It was observed preferential ozone attack to double carbon-carbon bonds in the main polymer chain for polyimide and polysulphone membranes. Polypropylene has single carbon-carbon bonds and its reaction with ozone was less intensive. For polydimethylsiloxane membranes the ozone attack seems to occur in the carbon-silicon bond, leading to loss of mechanical and thermal properties.