A 2 wt% copper catalyst supported on silica-pillared layered niobate (Cu/Si-Nb3O8) with a high hydrothermal stability was prepared and tested for the NO+CO reaction. Pretreatment with water vapor could improve the activity of the catalyst greatly, while the selectivity to N2 almost kept unchanged. The addition of water vapor (2 vol%) into the reaction gas could increase the activities of the catalyst without pretreatment and those pretreated by 2 vol% and 5 vol% stream, but reduce the activity of the catalyst pretreated by up to 10 vol% water vapor. Generally, water vapor in the reaction gas slightly reduced the selectivity to N2.