Abstract: The aim of this research was to investigate catalytic activity of Fe2O3 loaded activated carbon catalyst (Fe2O3/AC) prepared by the dipping method, and the effect of background constituents on catalytic ozonation of oxalic acid. Fe2O3/AC showed good activity in ozonation of oxalic acid, and the removal of oxalic acid was mainly based on catalytic contribution. Some background constituents such as HCO3-, CO32- and humic acid could cause the inhibition of oxalic acid degradation in Fe2O3/AC catalytic ozonation. The addition of HCO3-, CO32- increased the pH value of system, and therefore the activity of Fe2O3/AC decreased. The inhibition of oxalic acid degradation indirectly proved that catalytic ozonation of oxalic acid in the presence of Fe2O3/AC followed the mechanism of hydroxyl radical oxidation. The humic acid competed with oxalic acid to be adsorbed and oxidized which led to the inhibition of oxalic acid degradation.