The mechanical properties of hot-pressed, low-temperature-calcined α-alumina powder made from commercial aluminum hydroxide by seeding of wet grinding abrasion powder were investigated. The microstructure of samples sintered at low temperature is composed of very fine equiaxial grains and its bending strength is higher than 800MPa. As the sintering temperature increases, the grains become large and uniaxially elongated, the bending strength of sintered bodies decreases, and the fracture toughness increases. A sample sintered at 1400°C shows a bending strength of 600MPa and a fracture toughness of 7.9MPa⋅m^1/2 (SEPB method). A maximum fracture toughness of 9.0MPa⋅m^1/2 is achieved in a sample sintered at 1600°C. This high fracture toughness is caused by a uniform and elongated grain structure, and by increment of grain boundary fracture.