This invention relates to a process for preparing zirconium oxide, in its various forms, including zirconium-based mixed oxides. There is described a process for preparing a zirconium oxide in the absence of a cerium salt which comprises precipitating a zirconium hydroxide from an aqueous solution of a zirconium salt by reaction with an alkali in the presence of a controlled amount of sulphate anions at a temperature not greater than 50.degree. C. and then calcining the hydroxide to form an oxide, wherein the oxide thus formed is essentially sulphate free. Catalysts and ceramics can be produced from the product oxides having improved thermal stability and improved sinterability, respectively. A particular use of the product oxide is as a promoter or catalyst support in automobile exhaust systems.