Microwave-H2O2 (MW-H2O2) technology, one of the environmental treatment methods, was reported to usually prefer acidic and neutral circumstances in substrates' degradation. In this work, degradation of Rhodamine B (RhB) and methylene blue (MB) in MW-H2O2 system was found to be very competitive at extreme alkaline pH. This is a new finding and few studies have noticed it yet. Through radical species' tests and control experiments, degradation of RhB at strong alkaline pH in MW-H2O2 system was considered to mainly undergo oxygen oxidation, and the enhancement of MW thermal effect. This work provided a possible effective way to study the degradation at highly alkaline circumstances, and might promote the development of MW-H2O2 technology in alkaline wastewater treatment. (c) 2012 Elsevier B.V. All rights reserved.