The dielectric properties (εand tan δ) of aluminium oxynitride (AlON), and two grades of commercial alumina (99.9% and 97.5% A1203) have been measured after neutron irradiation doses to faiences ranging from 1017to 1020n/cm2. The measurements span the frequency range 0.1 to 65 MHz and thus include the ion cyclotron resonance frequencies currently being considered for plasma heating in fusion reactors. The permittivity (Ψ) has been measure by a two fluid technique with an accuracy of better than + / - 1%. A 2% increase in permittivity has been observed after irradiation to 1019n/cm2.