Abstract: A method of manufacturing .alpha.-alumina with a degree of purity of at least 98% which has a high sintering activity. The .alpha.-alumina contains at least 98% .alpha.-Al.sub.2 O.sub.3 and not more than 0.1% Na (calculated as Na.sub.2 O), and not more than 0.1% Ti (calculated as TiO.sub.2). The .alpha.-alumina also contains between 0.03% and 2% of Fe.sub.2 O.sub.3 and/or Cr.sub.2 O.sub.3. The .alpha.-alumina is formed by first fine grinding and then calcining, preferably at a temperature between about 1120.degree. C and 1350.degree. C, an aluminum hydroxide and/or hydrated aluminum oxide. The .alpha.-alumina is then cooled and finely ground to provide an .alpha.-alumina having excellent sintering activity.