In order to study communition in a jet mill, an experimental rig was built to investigate the breakage phenomena. Particles were accelerated with air in a nozzle to velocities ranging from 120 to 250 m/s and collided with a target. Energy loss during impact was evaluated by measuring particle velocities before and after impact. Two different systems for measuring particle velocities were implemented, ?The first one was designed to work at very low loading (particles are considered to hit the target individually). The velocities are measured by a high shutter speed video camera (up to 1 mu s) The particle traces on a frame were analysed by an image analyser. The second method, used for medium to high solid loading, consists of two sets of emitter-receptor optic fibres. Signals, collected by a 500kHz acquisition card, are cross-correlated in order to obtain the velocity. Influence of solid loading and initial air flowrate on characteristics of broken particles were evaluated, The influence of target nature and orientation were established.