When materials deform, damages accumulate. A theory,ecalled void damage theoryf,where damages are replaced with voids can express degradation of stiffness. However most models by the void damage theory neglect stiffness of particles which exist in materials and are one cause of damage. Since debonding along such particles creates new damage, it might be important to take into account the stiffness of the particles. In this study, the stiffness of particles or inclusions are considered by an averaging method, and the results are compared with experimental data to show eligibility of our model.