This study determines the potential of manganese oxide (MnOx) nanoparticles for the activation of peroxymonosulfate (PMS). The MnOx nanoparticles were prepared by a facile co-precipitation method and the degradation rates of acid red G (ARG) by the as-prepared catalysts in the presence of PMS were measured. The results showed that the Mn3O4 nanoparticles with tetragonal structure exhibited high catalytic activity for the degradation of ARG by activating PMS to generate radicals. The effects of the operational parameters on the catalytic property of the obtained nanosized Mn3O4 catalyst were investigated in detail. The catalyst exhibits excellent catalytic activity in a wide range of pH from 2 to 12. Moreover, it still maintained high catalytic activity even after five reaction cycles, indicating the good stability of the catalyst. In addition, radical quenching studies were carried out to ascertain the dominating radical species and a proper mechanism was also proposed. (C) 2015 Elsevier Inc. All rights reserved.