Ordered mesoporous Fe3O4 catalyst was successfully fabricated using KIT-6 as the hard template through a nanocasting route and innovatively investigated as a heterogeneous ozonation catalyst. The morphology and physico-chemical properties of as-prepared catalysts were characterized by X-way diffraction, Fourier transform infrared, transmission electron microscopy, X-ray photoelectron spectroscopy and N-2 adsorption-desorption techniques. Results showed that the surface area and average pore size of mesoporous Fe3O4 were 154.2 m(2) g(-1) and 6.2 nm, respectively. The mesoporous Fe3O4 catalyst presented superior catalytic activity for removing atrazine (ATZ) during ozonation compared to conventional Fe3O4 nanoparticles. The contribution of homogeneous ozonation reaction catalyzed by leaching irons was negligible, suggesting that the degradation of ATZ was mainly dominated by heterogeneous reaction catalyzed by mesoporous Fe3O4. Moreover, the removal rate of ATZ increased with the increase of catalyst dosage and solution pH. Based on the results of XPS analysis and radical scavenging test, a plausible mechanism was proposed. The redox cycles of Fe2+/Fe3+ was responsible for hydroxyl radical (OH center dot) generation and OH center dot dominantly contributed to the degradation of ATZ in this study. Finally, the possible transformation pathways of ATZ degradation were proposed and the toxicity of degradation products was evaluated. The results demonstrated that ordered mesoporous Fe3O4 is a promising catalyst for ozonation process, especially treating water polluted by ozone-resistant contaminants. (C) 2017 Elsevier B.V. All rights reserved.