The aim of this study is to investigate the behavior of mesotrione herbicide photodegradation under UV light irradiation with co-existence of iron oxides and oxalic acid. α-Fe₂O₃ and oxalate can set up a novel photo-Fenton-like system under UV irradiation in nature environment without H₂O₂ additional. The adsorption capacity of mesotrione was investigated in the dark by batch experiment, and the results were well fitted by Langmuir model. The effects of the iron oxide dosage, initial concentration of oxalic acid (C⁰_ox), mesotrione, and initial pH on the mesotrione photodegradation were investigated. The photoproduction of hydroxyl radicals (˙OH) during the photochemical process was also examined in diverse catalytic systems. The results indicated that mesotrione photodegradation follows pseudo-first-order kinetics. The mesotrione photodegradation moves slowly in the presence of α-Fe₂O₃ or oxalic acid. Interestingly, we found out that mesotrione photodegradation was distinctly enhanced when α-Fe₂O₃ and oxalic acid co-existed under UV irradiation. We learned that the combination of α-Fe₂O₃ and an oxalate system is an excellent agent to accelerate mesotrione herbicide decomposition. Results from this study could be further applied in the natural environment to facilitate environmental protection.