A MnOx–NbOx–CeO2 catalyst for low temperature selective catalytic reduction(SCR) of NOx with NH3 was prepared by a sol–gel method, and characterized by NH3–NO/NO2 SCR catalytic activity, NO/NH3 oxidation activity, NOx/NH3 TPD, XRD, BET, H2-TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy(DRIFTS). The results indicate that the Mn Ox–Nb Ox–CeO2 catalyst shows excellent low temperature NH3-SCR activity in the temperature range of 150–300℃. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NOx adsorption. As the NO2 content increases in the feed, water vapor does not affect the activity in NO2 SCR. Meanwhile, water vapor significantly enhances the N2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH4NO3 into N2O. A MnOx-NbOx-CeO 2 catalyst for low temperature selective catalytic reduction (SCR) of NO x with NH 3 was prepared by a sol-gel method, and characterized by NH 3 -NO / NO 2 SCR catalytic activity, NO / NH 3 oxidation activity, TPD, XRD, BET, H2-TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results that that Mn Ox-Nb Ox-CeO2 catalyst shows excellent low temperature NH3- SCR activity in the temperature range of 150 -300 ℃. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NOx adsorption. As the NO2 content increases in the feed, water vapor does not affect the activity in NO2 SCR. Meanwhile, water vapor significantly enhances the N2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH4NO3 into N2O.