Considering characteristics of breaking down H2O2 into water and molecular oxygen by catalase in waste activated sludge (WAS). the effect of H2O2 dosing strategy on sludge pretreatment by the advanced oxidation process (AOP) of microwave-H2O2 was investigated by batch experiments for optimizing H2O2 dosage. Results showed that the catalase in sludge was active at the low temperature range between 15 degrees C and 45 degrees C, and gradually lost activity from 60 degrees C to 80 degrees C. Therefore, the H2O2 was dosed at 80 degrees C, to which the waste activated sludge was first heated by the microwave (M), and then the sludge dosed with H2O2 was continuously heated till 100 degrees C by the microwave. Results at different H2O2 dosages showed that the higher the H2O2 dosing ratio was, the more the SCOD and total organic carbon (TOC) were released into the supernatant, and the optimum range of H2O2/TCOD ratio should be between 0.1 and 1.0. The percentages of consumed H2O2 in the AOP of microwave and H2O2 treating the WAS were 25.38%, 22.53%, 14.82%,13.61% and 19.63% at different H2O2/TCOD dosing ratios of 0.1, 0.5,1, 2,4, respectively. Along with the increasing H2O2/TCOD ratio, the contents of TCOD on particles, soluble substances and mineralization increased and the TCOD distribution on solids decreased. (C) 2009 Published by Elsevier B.V.