This paper reports an investigation of different persulfate (PS) activations, including PS at 20 °C (PS), thermally activated PS at 70 °C (T-PS), ferrous-ion activated PS at 20 °C [Fe(II)-PS)], hydrogen peroxide activated PS at 20 °C, and sodium hydroxide activated PS at 20 °C, for degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous phase. Several findings were made in this study including the followings: the 2,4-D degradation rates in T-PS and Fe(II)-PS systems were higher than other systems. However, complete degradation of 2,4-D and associated derivatives can be reached in all oxidation systems, with various reaction times. When considering the results of PS consumption during the 48 h reaction time to reach complete 2,4-D degradation, the T-PS system consumed all of the PS while only 10 % of the PS was consumed in the Fe(II)-PS system. The evaluation of optimum PS and ferrous ion doses indicated that under a fixed initial PS concentration, increasing Fe2+ concentration generally increased the amount of initial rapid degradation of 2,4-D and dissolved organic carbon. However, the effectiveness of the Fe(II)-PS system may be inhibited by the presence of excess iron. When a fixed level of Fe2+ was employed, various PS concentrations resulted in approximately equal 2,4-D degradation. The Fe(II)-PS system was found to be sensitive to the initial Fe2+ concentration, and the presence of soil revealed minor influence on the 2,4-D degradation by the Fe(II)-PS system. These findings indicate that the iron-activated PS process may be an effective method for remediating 2,4-D contamination.