Sintering behavior of granulated powder is investigated to develop a constitutive model for deformation analysis of ceramic powder compacts during sintering. Spray-dried alumina is compacted by CIPing (cold isostatic pressing) and sintered at various temperatures. Shrinkage and the change in grain size of the com­pacts during sintering are revealed in relation to the inhomogeneous microstructure consisting of fractured and unfractured granules as a consequence of the compaction. A constitutive model for the ceramic powder compacts having the internal structure is presented. The difference in grain growth in dense and sparse re­gions of the compacts is taken into consideration to the model. The results calculated by the model show good agreement with that obtained by experiment.