A series of catalysts of manganese oxides supported on multi-walled carbon nanotubes (MWCNTs) modified by oxygen dielectric barrier discharge plasma were prepared by the pore volume impregnation method, and the catalysts were characterized by TEM, XRD, XPS, N-2 adsorption, H-2-TPR, and Raman spectroscopy methods. The effects of Mn loading, calcination temperature, and MWCNTs outer diameter on selective catalytic reduction (SCR) of NO with NH3 were investigated, and the SCR activity tests were carried out in a fixed-bed reactor. The results showed that MnOx dispersion on MWCNTs varied with the Mn loading, calcination temperature, and MWCNTs outer diameter. Three states of manganese species (MnO2, Mn3O4, and MnO) coexisted in MnOx/MWCNTs catalysts, and most of the Mn existed as MnO2 and Mn3O4. Additionally, among the MnOx/MWCNTs catalysts prepared, MWCNTs (60-100 nm) supported 10 wt.% manganese calcined at 400 degrees C catalyst presented the best SCR activity under the conditions of 1000 ppm NH3, 1000 ppm NO and 5 vol.% O-2. Well dispersed MnOx on MWCNTs, high concentration of MnO2 and low concentration of MnO would lead to high SCR activity. (C) 2012 Elsevier B.V. All rights reserved.