Humic acids were degraded by ozone at room temperature in a stirred tank reactor and a fixed bed reactor with Fe/MgO catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids as compared to ozone alone. Fe/MgO was the most efficient catalyst to degrade humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that the humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight on the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed. The continuous reaction experiments with the palletized catalysts supported that humic acids can be removed by catalysis as well as adsorption.