Heat-activated peroxymonosulfate (PMS) has been widely accepted as an attractive approach in degrading organic contaminants.Nevertheless, heat/PMS process possesses poor performance on the removal of ammonia (NH+4-N).In this study, the commonly existing anion of chloride ion (Cl-) was employed to augment the removal of NH+4-N in the heat/PMS process.Heat/PMS/Cl- process possesses well performance on the removal of NH+4-N over the wide pH range of 3-11.The removal of NH+4-N in the heat/PMS/Cl- process adhered to the pseudo-zero order kinetic model, and kobs rose from 0.294 mg/L min-1 to 1.61 mg/L min-1 with the addition of 30 mM Cl- at pH 7.Chlorine (HClO), instead of HO, SO·-4, Cl and 1O2, was identified as the primary oxidant responsible for NH+4-N removal according to the quenching experimentsThe formation of HClO was proved to be mostly through the direct reaction between PMS and Cl-, rather than the reactions of reactive species with Cl-.The environmentally friendly gas of N2 predominated as the primary degradation product during the removal of NH+4-N with heat/PMS/Cl- process, although nitrite and nitrate nitrogen were also detected.Increasing Cl- concentration, PMS dosage and reaction temperature facilitated the removal of NH+4-N.Br- could significantly accelerate the removal of NH+4-N in heat/PMS/Cl- process.The other anions of SO2-4, CO2-3 and NO-3, the cations of Cu2+ and Fe3+, humic acid and landfill leachate had negligible effects on the removal of NH+4-N.Overall, this study offered an efficient approach to boost the oxidation capacity of heat/PMS process towards the removal of NH+4-N, and these findings had significant implications for the utilization of heat/PMS process in Cl--containing water.