The enhancement in dewaterability of waste activated sludge (WAS) by oxidative treatment using thermally- and alkali-activated persulfates (i.e., peroxymonosulfate (PMS) and peroxydisulfate (PDS)) was studied with two indices representing dewaterability change, i.e., centrifuged weight reduction (CWR) and standardized-capillary suction time (SCST). The tested conditions include 50 °C/PMS, 50 °C/PDS, 80 °C/PMS, and 80 °C/PDS as thermally-activated persulfate systems and NaOH/PMS, NaOH/PDS, KOH/PMS, and KOH/PDS as alkali-activated persulfate systems. The oxidation by activated persulfates caused the disintegration of bacterial cells and extracelluar polymeric substance (EPS) of WAS, affecting the sludge dewaterability. The highest dewaterability was found at the KOH/PDS treatment in CWR and at the 80 °C/PDS treatment in SCST. The EPSs were stratified as soluble, loosely-bound (LB) and tightly-bound (TB) fractions, and contents of protein and polysaccharide in each fraction were measured to characterize the EPS matrix before and after treatments. The statistical analysis of the relationship between EPS character and dewaterability indicated that the protein content in LB-EPS was the dominant negative factor for the dewaterability represented by SCST, whereas the polysaccharide content in soluble-EPS was identified as the dominant positive factor for the dewaterability by CWR