A catalyst for purifying exhaust gases includes an amorphous double-chained-structure type clay mineral with a transition metal element substituted for a constituent of the clay mineral, Mg and/or Al, a co-catalyst loaded on the clay mineral, and a noble metal element loaded thereon. The magnesium and/or aluminum are partially substituted by a transition metal element. The co-catalytic element is at least one element selected from the group consisting of rare-earth elements, alkali metal elements, and alkaline-earth metal elements. The catalyst can readily oxidize and decompose HC at low temperatures, and can inhibit the generation of sulfates, stemming from the magnesium and/or aluminum, at elevated temperatures.