Abstract: V₂O₅-MoO₃/ TiO₂ catalyst was prepared by sol-gel and impregnation method and modified with SiO₂ to improve its alkali-resistant performance. The alkali poisoning was simulated by the immersion of the catalyst in alkali salt solution. The effect of SiO₂ modification on the de-NO_xactivity of V₂O₅-MoO₃/ TiO₂ catalyst in the selective catalytic reduction was investigated. BET, H₂-TPR and NH₃-TPD measurements indicated that the specific surface area, the redox ability (the reduction temperature is decreased by 10 ℃) and the acidity of the SiO₂-modified V₂O₅-MoO₃/TiO₂catalyst are increased obviously. As a result, the alkali-resistant performance of V₂O₅-MoO₃/ TiO₂ catalyst was improved largely by the SiO₂ modification.