BrO3- formation from Br- containing drinking water ozonation treatment remains an important challenge. The inhibition mechanism of BrO3- formation was investigated during the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D) in mesoporous alumina supported MnOx (MnOx/Al2O3) suspension. The catalyst exhibited both significant inhibition of BrO3- formation and highly efficient catalytic ozonation of 2,4-D. Based on the characterization of UV-Vis spectrum, H2O2 determination and CV analysis, a redox process of bromine species occurred during the oxidation of 2,4-D in catalytic ozonation system. BrO3- reduction to Br- and the reduction of HBrO were responsible for the inhibition of BrO3- formation over MnOx/Al2O3 with ozone. An inhibition mechanism of BrO3- formation was proposed for catalytic ozonation in MnOx/Al2O3 suspension based on all experimental results. These observations will facilitate the development of catalytic ozonation for drinking-water treatment, especially for purification of Br- containing water. Crown Copyright (c) 2013 Published by Elsevier B.V. All rights reserved.