Ultrafine alumina powders with hydroxylated surfaces have been prepared by a technique similar to that which earlier yielded thixotropically active silicas. The method involves vaporization of alumina under reducing conditions from a plasma-heated centrifugal furnace, followed by oxidation with oxygen, water vapour, or carbon dioxide.The product is mainly γ-Al2O3 with an appreciable proportion of amorphous material. Surface areas measured by the BET method are in the range 100â 160 m² g^{â 1}, while a typical water-content determined thermogravimetrically was 5.5 % by weight. The factors controlling product properties are discussed, and these properties are compared with those of commercially available fine powders.