UV/chlorine, as an emerging advanced oxidation process, is able to degrade organic micropollutants in water via the generation of reactive oxidant species and direct reaction with HOCl/OCl- as well. In this study, light-emitting diodes (LEDs) were applied as the UV sources to investigate the efficacy of UV/chlorine process for the degradation of trimethoprim (TMP, a frequently detected antibiotic in waters), at slightly alkaline pH.