This invention relates to a cerium—zirconium-base composite oxide, which is useful, e.g., for the purification of exhaust gas discharged from combustion engines such as internal combustion engines and boilers and can release a high level of oxygen in a low temperature region, a method for producing the same, an oxygen storage/release component using the same, an exhaust gas purification catalyst, and an exhaust gas purification method. The cerium—zirconium-base composite oxide satisfies requirements (1) that the oxygen release initiation temperature is 380° C. or below, (2) that the oxygen release amount is not less than 485 μmol/g, and further (3) that the oxygen release amount at 400° C. is not less than 15 μmol/g. The cerium—zirconium-base composite oxide can be produced, for example, by mixing a starting material for cerium and a starting material for zirconium at a predetermined mixing ratio together, melting the starting material mixture at a temperature at or above the melting point, then cooling the melt to form an ingot, then optionally grinding the ingot to prepare powder, subsequently removing strain within powder crystal grains under heating, and then grinding to a further fine state.