The creep law of (Al2O3)1.8MgO single crystals has been experimentally derived from usual < 100 > compression creep tests in the temperature range 1 300 °C-1 450 °C. It obeys a so called dislocation creep equation : [MATH] which is consistent whith a glide creep controlled by dislocation climb. A well defined cell structure develops during creep, which is observed by Berg-Barrett topography, 1 MV and 100 kV electron microscopy both at the sample scale and at the dislocation scale. The features of this creep substructure is discussed in relation with the observed creep law