Particle breakage is the fundamental mechanism in all industrial comminution process. In this study, the breakage processes of particles with heterogeneous material property, irregular shape and size under various loading conditions are numerically investigated by the Rock Failure Process Analysis code (RFPA(2D)) from a mechanics point of view. The loading conditions include point-to-point loading, multipoint loading, point-to-plane loading, and plane-to-plane loading. The simulated results reproduce the particle breakage process: at the first loading stage, the particle is stressed and energy is stored as elastic strain energy with a few randomly isolated fractures. As the load increases, the isolated fractures are localized to form a macroscopic crack. At the peak load, the isolated fractures unstably propagate in a direction parallel to the loading direction following tortuous paths and with numerous crack branches. Finally, the major crack passes through the particle and several coarse progeny particles are formed. Moreover, in the vicinity of the contacting zone the local crushing is always induced to cause fines. On the basis of the simulated results, it is found that the dominant breakage mechanisms are catastrophic splitting and progressive crushing, which correspondingly result in progenies with two distinct size range: coarse particle and fines, respectively. It is pointed out that the particle breakage behaviour strongly depends on the heterogeneous material property, the irregular shape and size, and the various loading conditions. Because of heterogeneity, the crack propagates in tortuous path and crack branching becomes a usual phenomenon. Depending on the loading conditions, with the irregular shape and size used in this study, the particle strength increase but the energy utilization ratio decreases, and the particle behaviour has shown a brittle-ductile transition in a sequence of point-to-point loading, multipoint loading, point-to-plane loading, and plane-to-plane loading. (C) 2004 Published by Elsevier B.V.