This bench-scale study investigated the feasibility of activated persulfate (S2O82-) oxidation of methyl tertbutyl ether (MTBE), using pyrite (FeS2) as the source of ferrous ion activators. Under the FeS2-activated S2O82- condition, the sulfate free radical (SO4) is the predominant reactive species generated. The oxidation reactions were able to completely degrade MTBE when given sufficient doses of FeS2 and S2O82- and sufficient reaction time (e.g., 3 g FeS2/L and 5 g Na2S2O8/L within 4 h) and exhibited generation and subsequent degradation of the primary MTBE degradation intermediate products including tert-butyl formate, tert-butyl alcohol, methyl acetate, and acetone. The detailed reaction mechanism proposed for a SO(4)(-)driven oxidation process in this paper indicates that the destruction of MTBE most likely happens through alpha-hydrogen abstraction via attack of the SO4- at the intermediate methoxy group.