Two types of activated carbon (AC), namely Indonesian palm kernel shell-based AC (ZnCl2-AC) and commercial AC, were introduced to activate persulfate (PS) for catalytic degradation of methyl orange (MO) in water. This is the first attempt to apply the coupled sorption-oxidation kinetic model to the kinetic data of MO removal in the PS/AC system. The PS activated by AC removed more MO than the AC-only or PS activated by Fe2+. In the PS/AC system, to get maximum MO removal (100%), the use of commercial AC needed higher AC and PS dosages ([AC] = 185 mg L-1, and [PS] = 346 mg L-1) than the use of ZnCl2-AC ([AC] = 770 mg L-1, and [PS] = 1728 mg L-1). The MO removal in the PS/AC system fitted with the coupled sorption–oxidation kinetic model. Compared to the AC-only system, the PS/AC system enhanced the oxidation mechanism but depressed the sorption mechanism. The O2 •– played a dominant role in the oxidation mechanism. The MO was degraded through demethylation, carboxylation, ring opening, azo bond breakage, asymmetric cleavage, and aromatic ring removal.