Silicon-titanium mixed oxide powder prepared by flame hydrolysis, having a ratio by weight of silicon dioxide/titanium dioxide, which is greater on the surface of the primary particles than that within the total primary particle. It is prepared by a flame hydrolysis process, in that a stream consisting of a vaporous titanium dioxide precursor and oxygen or an oxygen-containing gas and hydrogen, and a second stream consisting of a vaporous silicon dioxide precursor and a carrier gas consisting of oxygen, an oxygen-containing gas and/or an inert gas, are guided separately into the reaction chamber of a burner such as is known for the preparation of pyrogenic oxides, and are burnt here, the solid mixed oxide powder and hot gases are subsequently cooled, and the gases are separated from the solid. The powder may be used, for example, for the preparation of sunscreen preparations.