Among many contaminants of emerging concern, perfluorooctanesulfonate (PFOS) is widely known as one of the most difficult to decompose due to a very strong carbon-fluorine bond. Electron beam technology has been used to treat refractory compounds as a radical-based advanced oxidation process. Therefore, the aims of this study were to investigate the degradation efficiencies of PFOS with various initial concentrations and radiolytic products generated by PFOS decomposition using an electron beam, to improve the decomposition efficiency of PFOS using combined persulfate (S2O82-) and hydrogen peroxide (H2O2) with an electron beam, and to propose the radiolysis decomposition pathway of PFOS in aqueous solution. The results showed that the degradation efficiency of PFOS by the electron beam depended on the initial PFOS concentration. The addition of S2O82- with the electron beam increased the decomposition efficiency with increasing absorbed doses. The 0.1 mg/L PFOS (0.19 mu M) in the presence of 5mM S2O82- with the electron beam at a 100 kGy absorbed dose had a similar decomposition efficiency with that using only the electron beam at a 900 kGy absorbed dose. However, the addition of H2O2 was ineffective on the PFOS degradation in aqueous solution. Seven radiolytic products such as perfluorocarboxylic acids (PFCAs) were quantitatively confirmed using authentic standards among eight predicted radiolytic products. The radiolysis decomposition of PFOS can occur spontaneously in aqueous solution with the synergistic effects of e(alpha q)(-) and center dot OH produced by electron beam irradiation. Therefore, the electron beam can be used as a viable process considering the decomposition efficiency and its degradation products.