Abstract AC-conductivity measurements were performed on aluminium oxynitrides (Alons) because of their interesting defect structure. Although it became apparent that these Alons are not stable in the temperature range used, the electrical properties of the materials could be measured with impedance spectroscopy using a special procedure. The activation energy for charge transport in Alons with 67.5, 73 and 77.5 mol% Al 2O 3 at temperatures between 1173 and 1373 K was 2.78, 2.85 and 2.97 eV, respectively, while the pre-exponential factors increased with increasing number of aluminium vacancies. The conductivity shows a more-than-linear dependency on the amount of aluminium vacancies. Charge is transported via aluminium vacancies but the large amount of vacancies does not result in greatly changed mobilities: the interesting defect structure of Alon does not lead to extraordinary electrical properties.