Boron nitride nanotubes (BNNTs)/alumina composites were fabricated by hot pressing. The effect of BNNTs on the mechanical properties, including ambient and high-temperature flexure strength and fracture toughness was investigated. As a result of sufficient physical and chemical bonding between BNNTs and alumina, the pullout and fracture of BNNTs concurrent with the suppression of BNNTs on abnormal growth of grains contributes to the excellent ambient and high-temperature mechanical properties.