<p>Slow hydrolysis is a major limiting factor in sludge anaerobic digestion. Thermally activated persulfate pretreatment has been used to promote the decomposition of sludge. However, the optimal activation temperature for persulfate-enhanced anaerobic digestion remains undetermined. This study investigated the effects of medium temperature-activated potassium persulfate (K₂S₂O₈) on the decomposition of waste activated sludge (WAS) and the performance of methane production. Pretreatment was conducted at three activation temperatures of 35&#xa0;°C, 55&#xa0;°C, and 75&#xa0;°C, with a K₂S₂O₈ dosage of 0.43&#xa0;g/g TSS for 1.5&#xa0;h. Results demonstrated that K₂S₂O₈ pretreatment significantly improved sludge hydrolysis rates and anaerobic digestion efficiencies of WAS. The soluble organic matter (SCOD) concentrations in WAS after pretreatment were 1372–2198&#xa0;mg/L, much higher than the control (521&#xa0;mg/L), and with optimal performance observed at 75&#xa0;°C. The methane production potential of pretreated groups increased by 67.4%, 94.6%, and 76.5% compared to the control, respectively, with the highest yield at 55 ℃. However, K₂S₂O₈ pretreatment delayed methanogenesis initiation, as indicated by the Gompertz model fitting result (lag phase λ: 1.21–2.60 d in treatment groups vs. &lt;0.1 d in the control). Although pretreatment also enhanced organic matter release during the anaerobic digestion stage, a considerable portion of dissolved organics remained unconverted to methane. Therefore, the impact mechanism of K₂S₂O₈ on anaerobic digestion needs further research. This study confirmed that medium temperature-activated K₂S₂O₈ pretreatment was effective for anaerobic digestion of WAS and more conducive to the stability of AD system.</p>