Process for preparing mixed oxides by reacting alkoxides of the elements titanium, zirconium, niobium, tantalum or mixtures thereof with metal hydroxides, metal carboxylates, metal hydroxycarbonates, metal carbonates or mixtures thereof of the elements lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc, cadmium, aluminum, gallium, yttrium, lanthanum, praseodymium, neodymium, samarium, dysprosium, europium, lead, bismuth or mixtures thereof in a C.sub.1 C.sub.8-alkanol, in a glycol ether or in a mixture thereof at from 50 to 200.degree. C.