A kinetic model was proposed and used to interpret the experimental data for degradation of Acid Orange 7 (AO7) in aqueous solution induced by Co 2+ /peroxymonosulfate (Co/PMS) reagent in terms of both decolorization and mineralization. The pseudo first-order decolorization rate constants are related to [Co 2+ ], [PMS], reciprocal of [H + ] and [AO7] 0 . Activation energy of the AO7 decolorization process was determined to be 75.7kJmol −1 . UV and visible light can accelerate the decolorization and mineralization process due to different mechanisms. In the combined UV/Co/PMS system, UV light can decompose PMS to generate hydroxyl (OH) and sulfate radicals (SO4-), while in the Vis/Co/PMS system, excited AO7 molecules can transfer electrons to PMS or Co 3+ and thus accelerate the decomposition of PMS and catalytic cycle of Co 3+ /Co 2+ .