Advanced oxidation processes based on sulfate radical (SO4 center dot-) have obtained great attention in water treatment and in-situ ground water/soil remediation. In this study, the degradation of chlorophenols (CPs) in Co2+ activated peroxymonosulfate (PMS) oxidation process was explored. It was found that 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol could be effectively removed in Co2+/PMS oxidation process. Presence of Br- greatly accelerated the transformation of the CPs, which can be explained by the formation of reactive bromine species including both bromine radical species and free bromine from the oxidation of Br- by SO4 center dot-. Br- could also be oxidized by PMS directly to form free bromine. Thus, degradation of the CPs was also observed in PMS oxidation process without any activators in the presence of Br-. Reactions between CPs and reactive bromine species resulted in the formation of brominated intermediates and disinfection byproducts (DBPs). Brominated phenolic intermediates such as Br2Cl-CP, BrCl2-CP, and Br2Cl2-CP were found in both Br-/PMS and Br-/Co2+/PMS systems. However, oxidized intermediates such as Br2Cl2-quinones were only identified in Br-/Co2+/PMS system. SO4 center dot- and radical bromine species are believed to be responsible for the formation of oxidized products. Bromoform and dibromoacetic acid were the main DBPs in both Br-/Co2+/PMS and Br-/PMS processes. Dichlorinated DBPs species, such as CHBrCl2 and dichloroacetic acid, were only found in Br-/Co2+/PMS system. Formation of dichlorinated DBPs suggests both dechlorination and chlorination reactions occurred, during which SO4 center dot- played a key role. The findings of this study indicate that presence of Br- can significantly facilitate the removal of organic contaminants but lead to brominated DBPs in PMS oxidation process, which should be taken into consideration when PMS is applied in environmental matrices containing Br-.