To provide a catalyst composition containing a novel perovskite-type composite oxide which permits reversible entrance and exit of noble metals, a catalyst composition is prepared so as to contain a perovskite-type composite oxide represented by the general formula (1): A x A' w B y B' (1-y-z) N z O 3±Ã (1) (wherein A represents at least one element selected from alkaline earth metals; A' represents at least one element selected from rare earth elements; B represents a tetravalent rare earth element; B' represents at least one element selected from transition elements (excluding tetravalent rare earth elements, Rh, Pd and Pt); N represents at least one element selected from Rh, Pd and Pt; x and w represent an atomic ratio satisfying the following relations: 0.8 x + w 1.3 (0.8 < x 1.3, 0 w 0.4); y represents an atomic ratio satisfying the following relation: 0 < y < 1.0; z represents an atomic ratio satisfying the following relation: 0 < z 0.5; and à represents an oxygen excess or deficiency amount).