Abstract: The composite oxide comprises, by weight, 100 parts of zinc oxide and at least one member, incorporated therein, selected from seven specific oxides in their specific amounts such as 0.001 to 5.0 parts of lanthanum oxide, 1.0 to 10.0 parts of cobalt oxide, 1.0 to 30.0 parts of titanium oxide, the composite oxide being surface treated with a silicone oil or a fatty acid to provide a surface-treated composite oxide of the present invention which has excellent ultraviolet screening capability and high visible light transmittance, these superior properties being well balanced with each other, and can maintain said superior properties over a long period of time. In one embodiment, there is provided a process for producing the ultraviolet screening surface-treated composite oxide.