The study focuses on the effect of microwave irradiation on sludge dewaterability. Capillary suction time and specific resistance of filtration were used to evaluate sludge dewaterability. Soluble chemical oxygen demand, extracellular polymeric substance (EPS) content and sludge particle size were determined in an attempt to explain the observed changes in sludge dewaterability. The results indicated that microwave application slightly enhanced sludge dewaterability with short contact time, while it significantly deteriorated sludge dewaterability with long contact time. The results show that 900W and 60s is an ideal microwave condition, yielding maximum sludge dewaterability characteristics by generating sludge with optimal disintegration (1.5–2%), EPS concentration (1500–2000mg/l), and particle size distribution (120–140μm).