Two series of gamma alumina samples have been characterized by means of the technique of thermoluminescence. The first one concerns products doped with various elements to a fixed concentration (1.5% refered to aluminum ions). The second one consists of alumina doped La³⁺ and Th⁴⁺ ions to a variable concentration between 0,5 and 4%. Two peaks thermoluminescence are present on all the samples. They are attributed to the presence of oxygen vacancies (358K) and hydroxyl ions (438K). The concentration of these two defects is shown to depend on the nature of the additive and its concentration