Peroxymonosulfate (PMS) activation has drawn increasing attention in eliminating the recalcitrant organic pollutants in water. Manipulation of generated reactive oxygen species (ROS) over Ce doped Mn2O3 during the PMS activation was firstly reported for the complete degradation of 2,4-dichlorophenol (2,4-DCP) in this study. Ce in-situ introduction can greatly enhance the PMS activation performance of Mn2O3. For example, 100% of 2,4-DCP degradation can be obtained at 90 min over 4 wt% Ce doped Mn2O3 at pH 7 (82.1% for Mn2O3 at 90 min). The reaction rate constant (k) was also about 3.6 times higher than that of Mn2O3 (0.0668 min(-1) for Ce doped Mn2O3 vs. 0.0186 min(-1) for Mn2O3). Besides O-1(2), center dot OH and SO4 center dot- were identified and involved in 2,4-DCP degradation process over Ce doped Mn2O3, while only O-1(2) was detected over 3D Mn2O3. Moreover, the contribution of center dot OH and SO4 center dot- to 2,4-DCP degradation can be regulated by adjusting the Ce doping amount. The key role of Ce substitution in the regulation of reactive oxygen species was further investigated by XPS and electrochemical experiments. The Ce dopant can lead to a higher current density and greater reductive capability due to the improved charge transfer capability, which is important to the generation of more aggressive center dot OH and SO4 center dot- and complete 2,4-DCP degradation.