A Ce—Zr mixed oxide is employed as an oxygen storage component for a lean-NOx catalyst, and catalytic precious metal atoms are placed at and/or between crystal lattice points of the mixed oxide. This structure prevents the sintering of the precious metal and accelerates movement of oxygen ions in each of crystallites of the Ce—Zr mixed oxide to increase the oxygen storage/release amount of the mixed oxide, which enhances the NOx removal performance of the catalyst.