Numerical simulations based on the discrete element method (DEM) were conducted to study the die compaction of iron ore fines and the mechanical strength of formed compacts under the uniaxial unconfined compression. To mimic the strength gained after the die compaction and brittle behaviour of compacts under compression, a bonded particle model was introduced between contacting particles. The simulated stress-strain responses were comparable with those observed from the physical experiments, confirming the validity of the model. The analyses of the evolutions of the structure and force during the die compaction indicated that the consolidation was initiated from the upper moving punch and gradually propagated to the lower stationary punch. The inhomogeneity of density and force trees was also observed. In the unconfined compression, the main characteristics of the stress-strain response, i.e., the linear increasing part, peak value and residual stress state, were captured in the simulations. The brittle failure of the compact was due to the broken inter-particle bonds by shear and tensile stress. The compressive strength of compacts increased with the consolidation pressure, bond thickness and bond strength. This work indicated that the DEM model with a proper interparticle bond model is able to study the mechanical strength of compacts. (C) 2015 Elsevier B.V. All rights reserved.