A micromechanical damage model is presented to predict the overall elastoplastic behavior and damage evolution in ductile matrix composites. The effective elastic moduli of three-phase composites are predicted by a micromechanical formulation. To estimate the overall elastoplastic-damage responses. an effective yield criterion is derived based on the ensemble-volume averaging process and the first-order effects of eigenstrains due to the existence of spherical inclusions. The effects of random dispersion of inclusions are accommodated. The proposed effective yield criterion, together with the assumed overall associative plastic flow rule and the hardening law, constitutes the analytical foundation for thr estimation of effective elastoplastic behavior of ductile matrix composites. An evolutionary interfacial particle debonding model is subsequently considered in accordance with the Weibull's statistical function to describe the varying probability of complete particle debonding. The interfacial debonding process is controlled by internal stresses of particles and a Weibull interfacial strength parameter. The completely debonded particles are regarded as voids for simplicity. The proposed elastoplastic-damage model is applied to the uniaxial, biaxial and triaxial tensile loadings to predict the various stress-strain responses. Efficient step-by-step iterative computational algorithms are also presented to implement the proposed damage model. Furthermore, the present predictions under various loading conditions are compared with other theoretical predictions and some available experimental data with modest particle concentrations. (C) 2000 Elsevier Science S.A. All rights reserved.