MoaMnTi10Ox (a= 0.2, 0.4, 0.6 and 0.8) catalysts have been prepared by sol-gel and applied in the NH3-SCR of NO reaction. These catalysts were characterized by XRD, H-2-TPR, NH3-TPD, XPS and in situ DRIFTS. Among the MoaMnTi10Ox catalysts, Mo0.6MnTi10Ox exhibits the excellent NH3-SCR performance with a broaden activity temperature window even in presence of 5 vol.% H2O, together with an excellent resistance of H2O and SO2. Compared with MnTi10Ox, the Mo addition leads to the reduction of redox ability, improvement of the surface acid sites and inhibition of NO adsorption. A serial of characterizations confirms that the synergistic effect between redox property and surface acidity plays a key role in the much better NH3-SCR activity over Mo0.6MnTi10Ox. Furthermore, the in situ DRIFTS studies reveal the NH3-SCR reaction is following the E-R mechanism over Mo0.6MnTi10Ox at 210 degrees C. In addition, the effects of H2O on the NH3-SCR reaction are investigated by in situ DRIFTS.