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This work studied the structural effects of hematite (α-Fe2O3), 2-line ferrihydrite (HFO) and goethite (α-FeOOH) on diethyl phthalate ester (DEP) degradation. The results showed that the degradation of DEP was faster under 365 nm light irradiation than in the dark in the presence of iron (hydr)oxides. The apparent kinetic rates of DEP degradation followed the order HFO ＞ goethite ≈ hematite in the dark and HFO ＞ hematite ＞ goethite under 365 nm light irradiation. Two pathways goved H2O2 decomposition efficiency on iron (hydr)oxide surfaces: (1) forming UOH on inherent surface hydroxyl groups (Fe-OH) and (2) producing O2 and H2O on the surface oxygen vacancies. X-ray photoelectron spectroscopy (XPS) analyses indicated that HFO not only has high Fe-OH content but also has high Vo content, resulting in its lowH2O2 utilization efficiency (η). DEP was degraded through hydrogen abstraction and deesterification, and the major products were (OH)2-DEP, mono-ethyl phthalate (MEP), OH-MEP, and phthalate acid (PA). The study is important in understanding the transformation of phthalate esters in top surface soils and surface waters under ultraviolet light.