Nanoscalar, pyrogenically produced yttrium-zirconium mixed oxide which has a BET surface area of between 1 and 600 m.sup.2/g, a total chloride content of less than 0.05 wt. % and does not exhibit a conversion into the monoclinic phase during storage is produced by atomizing yttrium compounds and zirconium compounds and reacting them in a flame. The mixed oxide can be used as ceramic raw material.