Quinclorac (QNC) is a widely used herbicide and is persistent in surface and ground waters. Its residuals and converted products are hazardous to aquatic animals, vegetation, and microbes, and it is therefore important to degrade QNC using an efficient and environmental friendly technology. In this study, the photocatalytical degradation of QNC using [(R,R)-(N,N'-bis(3,5,3' ,5' -tetra-tert-butylsalicylidene)-1,2-cyclohexanediaminato] manganese(III) acetate (Mn (III) salen) and H2O2 was performed under natural sunlight irradiation and a 91% degradation rate was achieved in neutral pure water in 240 min. The identified degradation products confirmed that the cleavage of QNC molecules was the main process involved in the hydroxylation, along with the cracking of the N=C bond on the pyridine ring and hydroxylation on the benzoic ring. The active species analysis showed hydroxyl radicals and superoxide radicals were the main reactive species. Photocatalytic kinetics indicated that the degradation process was in accordance with a pseudo-first-order kinetic equation.