Melatonin is a hormone, which may suppress the production of testosterome, decrease semen quality, and affect sexual activity and reproduction of animals and humans. Degradation of melatonin in aqueous solutions were investigated and compared by different advanced oxidation processes, including ultraviolet radiation (UV) alone, ultraviolet radiation assisted by hydrogen peroxide (UV/H2O2), Fenton's reagents (Fe2+/H2O2), and combination of Fenton's reagent with UV light (photo-Fenton, UV/H2O2/Fe2+). The experiments were conducted in a laboratory-scale batch photoreactor equipped with a 8 W low-pressure mercury lamp. The degradation of melatonin by all these processes was found to follow pseudo-first-order reaction kinetics. The effect of pH on the degradation of melatonin in the UV irradiation process was studied, and found that removal efficiencies of melatonin were 18%, 28% and 32% at 60 min and the rate constants were 0.0018, 0.0030 and 0.0048 min(-1) at pH value of 4.0, 7.0 and 10.0, respectively. The degradation efficiency of melatonin was greatly enhanced by UV/H2O2 process. Furthermore, effects of operating parameters (pH and concentrations of Fe2+ and H2O2) on the degradation of melatonin by Fenton's reagent were investigated, and the degradation of melatonin was more efficient by Fenton's reagent than by UV/H2O2 process. The fastest degradation of melatonin and highest TOC removal was achieved by UV/Fe2+/H2O2 process among the four different processes tested. (C) 2009 Elsevier B.V. All rights reserved.