Grain boundary sliding (GBS) is thought to be the principal driving force for the nucleation, growth, and coalescence of grain boundary cavities during compressive creep of polycrystalline ceramics. It has been shown theoretically that stochastic GBS gives rise to continuous cavity nucleation and transient cavity growth and coalescence, eventually leading to crack formation and failure. This paper will show through experimental measurements, using stereoimaging techniques, that GBS is in fact stochastic. Also, mode II GBS, in‐plane grain rotation, and in‐grain shear displacements, strains, and strain rate measurements during creep of Lucalox Al2O3will be presented. These displacements, measured on a machine vision system, will be presented in terms of the surrounding microstructural constraint and their lack of angular relation to the compressive load a