A holding and sealing material for disposal between a catalyst carrier and a metal shell covering the outer face of the catalyst carrier. The holding and sealing material includes an inorganic fiber mat subjected to needle punching producing needled holes having a density of 50-3,000 per 100 cm2 thereof and an organic filler included inside of the needled holes of the inorganic fiber mat. The holding and sealing mat material generates a surface pressure of 5-500 kPa when heated to 300-1,000° C. under the filling bulk density of 0.15-0.45 g/cm3. The holding and sealing mat material includes an organic component which is over 0 and not more than 2 weight % after being heated to 300-1,000° C.