The present work reported a modified persulfate activation process with a microbial siderophore named desferrioxamine B (DFOB). DFOB was a natural complexing agent and could complex with Fe3+ strongly. The photochemical reactivity of Fe(III)-DFOB was studied. Fe2+ and HO• were produced from Fe(III)-DFOB photolysis. Furthermore, the degradation of atenolol (ATL) was followed in light/persulfate (PS)/Fe(III)-DFOB system. The main oxidative radicals were SO4 •− in this system. The results of pH effect showed that there was no obviously fluctuation on ATL degradation efficiency with the pH increased from 2.5 to 8.4. Moreover, kSO4•−,DFOB was determined by laser flash photolysis (LFP) experiments. DFOB had positive effect on Fe2+ formation but negative effect on ATL degradation due to the high react rate constant between DFOB and SO4•−. The effects of chloride and carbonate ion were also investigated. The results in this study proposed the reaction mechanism of the modified persulfate activation process, and it could be applied in neutral and weak-alkaline pH range.