Anaerobic stabilized landfill leachate was treated by persulfate (S2O82−) oxidation. The effect of three factors namely; persulfate dosage, pH and reaction time on COD and NH3-N removals; was studied. The results of analysis of variance (ANOVA) showed that the selected factors significantly affected the percentage of COD and NH3-N removals. Furthermore, the maximum removal was achieved at 60 min of persulfate oxidation, a COD/S2O82− ratio (1 g/4.2 g), and pH7, the percentage of removals for COD and NH3-N were 45% and 55%, respectively. The effect of persulfate oxidation on the biodegradability of leachate was also investigated. The results showed that the BOD5/COD ratio improved from 0.09 to 0.1. The oxidation enhanced the biodegradable (CODbi) from 36% to 57%. Hence, persulfate is suitable to pre-treat highly-concentrated stabilized leachate. This process should follow the organic degradation and ammonia removal followed by biological treatment processes.