The creep properties of polycrystalline A12O3(grain size 14 to 65 μm) were examined under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C. Two distinct types of behavior were observed. The creep rate of medium‐grained specimens (14 to 30 μm) could be described by ασ1.2/d2where σ is the applied stress anddis the grain size. These results are consistent with the Nabarro‐Herring creep mechanism. For the coarse‐grained (65 μm) specimens, the creep rate was related to the stress by ασ2.6. This behavior was not related to cracking; instead, a dislocation mechanism was thought to be rate‐controlling. Considerable evidence for grain‐boundary sliding was seen, and measurements showed that grain‐boundary sliding contributed between 46 and 77% of the total strain in the 3 medium‐grained specimens examined and between 38 and 50% in the 3 coarsegra