The low molar absorption coefficient of HO limits the ultraviolet (UV)/HO process, making it a desirable target to enhance the UV/HO process for organic micropollutant degradation. Therefore, this study investigated the impact of iron-containing coagulants (Fe-coagulants) on micropollutant degradation by UV/HO process. Three typical Fe-coagulants (i.e., polymeric ferric sulfate, polymeric aluminum ferric sulfate, and FeCl) exhibited the enhancement of sulfamethazine degradation during the UV/HO process. The maximum increasing ratio of the degradation rate constant reached 40%. The pH and Fe-coagulant concentration effects, as well as residual HO were examined. The principal mechanism of micropollutant degradation enhancement via the Fe-coagulants was the photo-Fenton-like reaction between Fe(III) on the Fe-coagulant surface and HO under UV irradiation. Then the influence of Fe-coagulant particle size was discussed. Smaller particles (<0.22 μm), with a lower iron content, a larger specific surface area, and a stronger optical scattering effect, exhibited a greater enhancement on the UV/HO process as compared with larger particles (>0.22 μm). Finally, the enhancement effect of the Fe-coagulants was verified on two water samples from a water treatment plant, which were either pre-coagulation or sand filtered samples. This study explored an existing heterogeneous catalysis process in drinking water treatment, which provides additional information for coagulant selection and improvements to the treatment process for micropollutant removal.