In this research, we choose photolysis degradation (PD) course and H2O2-enhanced PD (HPD) course using UV-vis light from two microwave-powered electrodeless discharge lamps (MPEDL-2) as simplified models. The results verified that (1) similar to 70% and 99.7% of MG were removed in PD and HPD courses within 5 min irradiation, and PD course was proved to be dependent on center dot OH and O-2(center dot-), (2) major routes were related to transformation of MG into malachite green carbinol base (MGCB), which could be further decomposed into 4-dimethylaminobenzophenone (DLBP), and (3) after 0.5 min irradiation, PD course verified that similar to 30% and 1% of MG was converted into MGCB and DLBP; for comparison, HPD course demonstrated that similar to 12.9% and 28.5% of MG was transformed into MGCB and DLBP. Accordingly, we draw conclusions that degradation mechanism of MG could be revised as seven steps with MGCB as a key product and pH variation of aqueous dyes solution played minor role. Additionally, these conclusions were also enlightened for degradation of MG by advanced oxidation process. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.