A catalyst assembly includes a housing having at least first and second recesses with side surfaces, and a catalyst carrier body fixed in said housing. The catalyst carrier body has a casing tube and a honeycomb body through which an exhaust gas can flow. The casing tube has at least first and second protuberances with side surfaces and said casing tube is connected to said honeycomb body at least in a partial region. The protuberances extend at least partially into said recesses to form a fixed mounting and at least one floating mounting with an axial mounting play. The assembly ensures that the catalyst carrier body is permanently fixed, in particular during structure-borne vibrations that occur in the exhaust system of an internal combustion engine.