The activated carbon-supported manganese oxides (MnOx/GAC) was utilized for catalytic ozonation of heavy oil refinery wastewater (HORW). MnOx/GAC was characterized by XRD, SEM & EDS, TGA and N-2-adsorption-desorption. The effects of reaction parameters on HORW treatment were investigated. COD, BOD5, TOC, biodegradability, toxicity, simulative activated sludge processes and ESI-FT-ICR MS analysis were used to analyze HORW samples. MnOx/GAC exhibited greater COD reduction efficiency in the catalytic ozonation of HORW than did GAC. The dominant mechanism of HOPW catalytic ozonation was oxidation via hydroxyl radicals over MnOx/GAC. The results suggested that big molecular pollutants with high toxicity and low biodegradability were first degraded to small molecular oxidation products with low toxicity and high biodegradability, afterward which small molecular pollutants and oxidation products further oxidized or mineralized. The investigation uncovered the industrial potential of MnOx/GAC for ozonadon treatment of refinery wastewater. (C) 2014 Elsevier B.V. All Rights Reserved.