Abstract Measurements have been made of the angular correlation N(θ) of positron annihilation quanta, the triquanta annihilation intensity I 3γ by the peak-to-peak method, and the average lifetimes of positrons in A1 2O 3. The measured quantities depend on the temperature at which the Al 2O 3 was obtained. It is assumed that there are two conversion centers of ortho -Ps. One is molecular oxygen adsorbed on the oxide surface and the other is the O − ion which exists in A1 2O 3 obtained at lower temperatures, both on the surface and in the interior of the grains. The temperature ranges have been determined within which the changes in properties of the oxide with respect to the annihilation of positrons, occur slowly as well as those within which the changes occur rapidly. Among these properties are the vanishing of the postulated O − ions with rise in temperature a probable diffusion of aluminium ions, and the vanishing of vacancies in the lattice structure (I Ps). From the measurements of the rate characteristics the complete annihilation intensity I xxx was calculated within the range from 0.34 to 96ns, and also annihilation intensity from para states of positronium I p .