Since the difference between oxygen‐ion and cation diffusion coefficients is greater for α‐Cr2O3than for α‐Fe2O3or α‐Al2O3, a study of initial‐sintering kinetics was undertaken to show unequivocally which species is rate controlling. Fine powders of α‐Cr2O3, obtained by thermal decomposition of reagent‐grade (NH4)2Cr2O7, were lightly compacted and their isothermal rates of shrinkage were determined between 1050° and 1300°C. Resultant data follow volume‐diffusion sintering models, and calculated diffusion coefficients agree with, those measured for oxygen ions in α‐Cr2O3. There is little evidence that oxygen diffusion along grain boundaries becomes so enhanced that chromium ions are left i