The removal of Rhodamine B (RhB) by CoxFe3-xO4 magnetic nanoparticles activated Oxone has been performed in this study. A series of CoxFe3-xO4 nanoparticles was synthesized using a hydrothermal method. The synthetic CoxFe3-xO4 nanoparticles were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that they were spinel structures and Co was introduced into their structures. The performances of CoxFe3-xO4 nanocatalysts on the activation of Oxone for removal of RhB were investigated and we found that the higher cobalt content in the catalyst, the better removal performance was resulted. A series experiments of reaction conditions were also performed, which confirmed that weak acidic, higher temperature, higher dosages of CoxFe3-xO4 nanocatalyst and Oxone and lower concentration of RhB were favored for the degradation of RhB. The pseudo-first order kinetics was observed to fit the CoxFe3-xO4/Oxone process. Furthermore, the reaction mechanism was discussed and the scavenging effect was examined by using phenol and tert-butyl alcohol which indicated that sulfate radicals were the dominating reactive species responsible for the degradation process. Finally, the stability of CoxFe3-xO4 nanocatalyst was studied. (C) 2012 Elsevier B.V. All rights reserved.