Sulfonamides (SAs), commonly used as human and veterinary antibiotics, are of great concerns because of their frequent detections in aquatic environment. This study investigated the oxidation of six SAs (i.e., sulfamethoxazole (SMX), sulfamethizole, sulfamethazine, sulfadimethoxine, sulfamerazine, and sulfathiazole) by chlorine dioxide (ClO2). The results indicate that the reactions followed the second-order kinetic model, with rate constants ranging from 3.85 x 10(3) to 2.59 x 10(4) M-1 s(-1) at pH 7.0 and 20 degrees C. For each SA, the rate constant increased by 1.6-2.2 orders of magnitude as the solution pH increased from 4.0 to 9.5. The activation energies of the selected SAs ranged from 31.6 to 39.8 kJ mol(-1). In addition, SMX was selected as a model compound to explore the degradation pathways during ClO2 oxidation. The reactivity of SMX toward ClO2 was strongly related to the ionization equilibrium of the amido-nitrogen in SMX molecule. The cleavage of SAN and CAS bonds and the hydroxylation of aniline moiety in the SMX molecule constituted the major degradation pathways. ClO2 oxidation was likely to decrease the antibacterial activity of SMX solution because of the destruction of p-aminobenzenesulfonamide moiety. The obtained rate constants could well predict the fate of SAs during ClO2 oxidation in a surface water, where an effective removal of SAs by ClO2 can be expected under practical water treatment conditions. (C) 2017 Elsevier B.V. All rights reserved.