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Degradation kinetics, byproducts and mechanism for trichloroacetic acid were analyzed in an efficient TiO 2 photocatalytic process combined with Fenton reagent. Modified pseudo first-order kinetics was firstly established and it was more rigorous than the real first-order kinetics, and then the apparent rate constant was calculated and it mainly influenced by initial concentration of TCAA, aqueous solution pH and the dosages of Fe 2+ and TiO 2 . Intermediated byproducts detected with ion chromatography, high performance liquid chromatography and gas chromatography methods were mainly Cl − , dichloroacetic acid, monochloroacetic acid, acetic acid, formic acid and CO 2 in aqueous solution. To analyze the tracks of carbon and chlorine elements, main byproducts were quantified and the mass balance for carbon and chlorine elements was established. Mineralization of TCAA was 92% after 5 h and the final product is CO 2 and HCl. Degradation mechanism involving dechlorination, decarboxylization and oxidation was achieved, and the major degradation pathway was as follows: trichloroacetic acid → dichloroacetic acid → formic acid and monochloroacetic acid → formic acid and acetic acid → formic acid → CO 2 . [ABSTRACT FROM AUTHOR]