The effect of ultrasound assisted Fenton (US/Fenton) treatment on the physicochemical properties of textile dyeing sludge was investigated in this paper. The sludge particle size, total organic carbon (TOC), extracellular polymeric substance (EPS) concentration and sludge disintegration degree (DDSCOD) were measured in an attempt to understand the observed changes in sludge physicochemical properties. The results showed that the US/Fenton-treated sludge presented obvious advantages over the Fenton-treated sludge for disrupting sludge floc structure. The suitable condition for sludge disintegration was found to be 0.12-0.16 W/ml (ultrasonic density) and lower pH (<= 3), under which the TOC in soluble phase increased obviously by releasing organic substances of sludge flocs. The changes of sludge dewaterability were dependent on sludge disintegration during US/Fenton treatment. The optimal EPS concentration and DDSCOD to obtain maximum sludge dewaterability were found to be 90-100 mg/l and 4-6%, respectively. After 10 min of Fenton and US/Fenton treatment, the hydroxyl radical (center dot OH) was 2.71 mu mol/l and 2.90 mu mol/l, respectively, which confirmed that US/Fenton treatment had a synergetic effect. (C) 2013 Elsevier B.V. All rights reserved.