A novel microwave electrodeless lamp (MWL) rather than traditional electrode lamp (TEL) was used in a H2O2/MWL system as light source. This technique provided a new way to study the simultaneous effect of both UV-vis light and microwave irradiations. This study showed that H2O2/MWL process was 32% more effective than H2O2/TEL process in degrading azo dye Acid Orange 7 (AO7). Further study found that the degradation of AO7 by the H2O2/MWL process was initiated by the attack of HO. radicals generated by the photolysis of H2O2. However, the direct photolysis of AO7 by MWL irradiation was not negligible. Effect of operation parameters, such as the initial concentrations of A O7 and H2O2 and pH. were investigated. A kinetic model of degradation of AO7 by H,O-2/MWL process was found, in which not only the HO. oxidation but also direct photolysis were considered. The kinetic model was consistent with the experiment results. The degradation of AO7 by H2O2/MWL corresponded to a pseudo-first order reaction. The apparent reaction constant (k(ap)) was a function of initial concentrations of H2O2 and AO7 and pH of the solution. (c) 2005 Elsevier B.V. All rights reserved.