The effectiveness of low temperature ozone treatment for organic template removal from MFI zeolite membranes was investigated. The aim is to establish a convenient and reliable method for zeolite membrane activation that will ensure not only high gas permselectivity but also more importantly, good reproducibility. Fifty ZSM-5 zeolite membranes were prepared for the study. The effects of ozone concentration, treatment temperature, membrane thickness and compositions on the treatment process were examined. Half an hour treatment in oxygen mixture containing 50g/m(3) of ozone at 473 K is sufficient to remove all organic templates from 2 mum MFI zeolite membranes. Longer treatment time is needed for thicker membranes and for ZSM-5 with high aluminum concentrations. Membranes with excellent gas permeance and permselectivity were consistently obtained using this treatment method. Also, the membranes treated by ozone exhibit more reproducible membrane properties. (C) 2004 Elsevier B.V. All rights reserved.