In this study, the degradation efficiencies and mechanisms of atrazine, a recalcitrant herbicide, were thoroughly investigated using ferrate (Fe(VI))/peroxymonosulfate (PMS) process. In comparison with Fe(VI) or PMS alone, Fe(VI)/PMS process significantly enhanced the degradation of atrazine, and its degradation efficiency was higher than that of Fe(VI)/persulfate or Fe(VI)/H2O2 process at pH 6.0. Complete degradation of atrazine at an initial concentration of 46.5 mu M could be achieved within 20 min at initial concentrations of 6.0 mM Fe(VI), 5.0 mM PMS, pH 6.0, and 25 degrees C. Fe(VI)/PMS could efficiently degrade atrazine within a wide range of pH values (5-9). NOM concentration lower than 4.0 mg/L was favorable for atrazine degradation. Results of electron spin resonance and quenching studies indicated that both hydroxyl radical and sulfate radical were generated in the Fe (VI)/PMS process, while sulfate radical was the dominant reactive radical responsible for atrazine degradation. The mechanisms of PMS activation were elucidated on the basis of the results of XRD and XPS. In addition, fourteen intermediates from atrazine degradation were identified by LC/MS/MS, and consequently pathways for the degradation were proposed.