Three typical fluoroquinolones (FQs), ciprofloxacin, norfloxacin and enrofloxacin were degraded using the thermal activation of persulfate (PS). The degradation rates of FQs generally increased with the rise of PS/fluoroquinolone ratio (20:1-80:1) and temperature but decreased with the increase of initial pH values. The major degradation mechanisms of fluoroquinolones by thermally activated PS were proposed. Abundant intermediates identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that the oxidation would occur mainly on the C-F bonds (for ciprofloxacin and enrofloxacin) or the C-H (for norfloxacin) bonds on the quinolone, groups, causing hydroxyl substitution as well as hydrogen abstraction, and on the piperazine groups following a series of substitutions, additions and eliminations resulting in the final open-loop reactions. (C) 2016 Elsevier B.V. All rights reserved.