Distortions or cracking in metal/ceramic graded powder compacts during sintering may be caused by the variation in densification behavior of the layers with different mixing ratios. To clarify the constitutive response of the heterogeneous powder compacts, a micromechanics model for sintering is proposed. The sintering stress as well as the viscosity of the powder mixtures is expressed by using Eshelby's equivalent inclusion method and Mori-Tanaka's mean-field theory. The variation in sintering behavior with metal/ceramic mixing ratio computed by the proposed model is compared with the experimental data for Ni/Al2O3 system. The present model can reproduce the decrease in sintering rate of the powder mixtures, which remarkably appears in the Ni/Al2O3 powder compacts with small amount of Al 2O3.