AbstractÐCompressive plastic deformation of particle-reinforced metal±matrix composites is investigated through numerical modeling at high rates of strain. The numerical modeling is performed using axisymmetric unit cell models, with the particles treated as elastic ellipsoids or cylinders embedded within a viscoplastic matrix. The constitutive behavior of the matrix material uses a power law strain-rate hardening formulation and is obtained from independent experimental results on the matrix. The ¯ow stress of the composites is predicted over a range of strain rates for dierent particle volume fractions and for varying particle shapes and particle aspect ratios. The results show that both the ¯ow stress and the strain-rate hardening increase with increasing volume fraction of the reinforcement. It is also shown that the ratedependent ¯ow stress is in¯uenced not only by particle aspect ratio but also by particle shape (spheroidal or cylindrical). A simple analytical model has been constructed that is able to capture the quantitative features of the computational predictions. Both computational and analytical models have been compared with experimental data on two dierent composites from two dierent sources in the literature, with excellent quantitative agreement on the rate-dependent stress±strain behavior.