An ammonia oxidation catalyst (AMOX) for oxidizing and removing surplus ammonia, in selectively reducing nitrogen oxides by adding urea or ammonia as a reducing agent of the nitrogen oxides and using a selective catalytic reduction catalyst, into exhaust gas discharged from a lean-burn engine, comprising by coating at least two catalyst layers having a lower layer comprising a catalyst supported noble metal element on an inorganic base material which is any of a composite oxide powder having at least titania and silica as main components, alumina, and a composite oxide powder consisting of alumina and silica, wherein the composite oxide powder comprises titania in an amount of 60 to 99% by weight and silica in an amount of 1 to 40% by weight, and an upper layer comprising a composite oxide powder consisting of silica, tungsten oxide, ceria, and zirconia, at the surface of an integral structure-type substrate, characterized in that a composition of the composite oxide powder is silica: 0.1 to 5% by weight, tungsten oxide: 3 to 30% by weight, ceria: 5 to 40% by weight, and zirconia: 50 to 90% by weight; a content of the noble metal element to be supported on the inorganic base material being any of the composite oxide powder, alumina, and the composite oxide powder, is 0.01 to 1.0 g/L per unit volume of the integral structure-type substrate; a coated amount of the inorganic base material being any of the composite oxide powder, alumina, and the composite oxide powder of the catalyst layer (lower layer), is 10 to 60 g/L per unit volume of the integral structure-type substrate; a coated amount of the composite oxide powder of the catalyst layer (upper layer), is 15 to 120 g/L per unit volume of the integral structure-type substrate; and the noble metal element is one or more kind of element selected from platinum, palladium, or rhodium. comprising by coating at least two catalyst layers having a lower layer comprising a catalyst supported noble metal element on an inorganic base material which is any of a composite oxide powder having at least titania and silica as main components, alumina, and a composite oxide powder consisting of alumina and silica, wherein the composite oxide powder comprises titania in an amount of 60 to 99% by weight and silica in an amount of 1 to 40% by weight, and an upper layer comprising a composite oxide powder consisting of silica, tungsten oxide, ceria, and zirconia, at the surface of an integral structure-type substrate, characterized in that a composition of the composite oxide powder is silica: 0.1 to 5% by weight, tungsten oxide: 3 to 30% by weight, ceria: 5 to 40% by weight, and zirconia: 50 to 90% by weight; a content of the noble metal element to be supported on the inorganic base material being any of the composite oxide powder, alumina, and the composite oxide powder, is 0.01 to 1.0 g/L per unit volume of the integral structure-type substrate; a coated amount of the inorganic base material being any of the composite oxide powder, alumina, and the composite oxide powder of the catalyst layer (lower layer), is 10 to 60 g/L per unit volume of the integral structure-type substrate; a coated amount of the composite oxide powder of the catalyst layer (upper layer), is 15 to 120 g/L per unit volume of the integral structure-type substrate; and the noble metal element is one or more kind of element selected from platinum, palladium, or rhodium.