Thermomechanical properties of a spinel-ferrite-based cermet, envisaged to built inert anodes for the Hall-Heroult processing of aluminium, have been intensively investigated before and after full oxidation under air. At low temperatures, the behaviour is purely linear, elastic and brittle. Above 900 A degrees C, the material creeps and exhibits a very large ductility for a ceramic-based material. Elasticity, fracture and viscoplasticity have been characterised up to 1000 A degrees C using compression and bending tests. A non-linear isotropic strain hardening creep law has been identified using an optimisation procedure coupled with a finite element analysis of the bending creep tests. Microstructural, physical and mechanical changes induced by full oxidation have been characterised.