Oxidation induced by potassium persulfate was evaluated as an economic substitute for the Fenton-like reaction for the purpose of rice straw pretreatment in terms of temperature (80–140 °C), potassium persulfate concentration (5–100 mM) and process time (0.5–3 h), an optimal pretreatment condition was identified: 120 °C for 2 h with 75 mM potassium persulfate concentration and yielded 91% enzymatic digestibility using 25.2 FPU/g of biomass. Crystallinity index, SEM and SEM-EDS analyses revealed that biomass was indeed disrupted and components like silica were exposed. All this suggested that this persulfate-based pretreatment method, which is distinctively advantageous in terms of effectiveness and economics, can indeed be a competitive option.