Abstract: The present invention aims at providing a novel NOx-decomposing catalyst and a denitrification method using the same. The feature thereof consists in an NOx-decomposing catalyst, in which vanadium oxide is supported on titanium oxide of anatase type, having a specific surface area of 100 to 250 m.sup.2 /g and micro pores of 15 to 25 .ANG. in pore diameter and 75 to 85 .ANG. in pore diameter respectively in an amount of at least 0.05 cc/g, and a method for the denitrification of a waste gas comprising contacting an NOx-containing waste gas with the above described catalyst in the presence of a reducing gas at a temperature of 100.degree. to 350.degree. C. An NOx-containing waste gas with coexistent catalyst-poisonous materials such as water, SOx, etc. can be treated in an effective manner at a relatively low temperature, e.g. 170.degree. C. or lower, at which no practical treatment can be carried out by the prior art method, without formation of N.sub.2 O as a by-product.