Nanosized CaO2 was first synthesized using montmorillonite clay layers as templates for combining the positive effects of filtration aid and peroxidation on the dewatering of waste-activated sludge (WAS). Exchangeable Ca2+ compensating for negative charges of montmorillonite reacted with the added H2O2, affording nano CaO2 on the surface or in the interlayer regions of montmorillonite (montmorillonite-supported nano CaO2, MMT-nano CaO2). The catalytic capacity of montmorillonite for generating (OH)-O-center dot from nano CaO2 was verified by electron paramagnetic resonance (EPR), therefore, the radical oxidation induced by MMT-nano CaO2 can destruct the floc structure of WAS with the omission of Fe(II), the conventionally used catalyst for Fenton reaction. As a result, the reduction in specific resistance of filtration (SRF) by 62.2% was achieved with the MMT-nano CaO2 dosage of 100 mg/g dry solid (DS) and the weakly acidic pH of 5. (OH)-O-center dot led to the reduction of hydrophilic protein in extracellular polymeric substances (EPS), and the swelling behavior of montmorillonite contributed to the formation of a porous structure as draining medium for water withdrawing. The above factors were the dominant mechanisms for enhancing dewatering performance. (C) 2016 Elsevier B.V. All rights reserved.