The degradation of ortho-chlorophenol using Fenton's reagent was studied by chemiluminescence(CL).Without a special CL reagent,a weak CL emission from the mixture of ferrous ion and hydrogen peroxide was observed at room temperature.The CL intensity was increased by the addition of ortho-chlorophenol into the mixed solution.When the temperature was raised to 65℃,the CL intensity was enhanced strongly.The CL mechanisms for the system H2O2-Fe2+ with and without ortho-chlorophenol were studied by examining the CL spectrum,gas chromatography-mass spectrometry and electron spin resonance spectrum.The effects of various free radical scavengers,surfactants and fluorescence compounds on the CL intensity were also investigated.A self-catalytic oxidation mechanism was proposed.The results showed that singlet oxygen was the main emitter for the system H2O2-Fe2+.The strong CL from the system H2O2-Fe2+-ortho-chlorophenol was due to singlet oxygen and electronically excited quinone.The benzenediol-like intermediate product formed during the phenol oxidation process greatly promoted the Fenton's reaction and led to higher CL intensity.Chemiluninescence is a novel approach for the investigation of the oxidation of some organic pollutants by Fenton's reagent.