The cold isostatic pressing behaviour of aluminium and iron powders was analysed, both experimentally using a cold isostatic pressing unit, and numerically using a nonlinear finite element program. The pressing unit, which can withstand up to 650 MPa pressure was designed and constructed in this study. Aluminium and iron powders, having different hardness values and almost the same particle sizes, have been pressed in the pressure unit and the mechanical behaviours of these powders were investigated in the 100-500 MPa pressure range. Attained densities were about 98% for aluminium and 88% for iron powders. Pressing resulted in significant increases in microhardnesses of the aluminium and iron powders. Light and scanning electron microscopy examinations revealed that severe plastic deformation took place in the powders of aluminium and iron. The densification behaviour of aluminium and iron powders under the cold isostatic pressing was also analysed using the finite element method, in which an elasto-plastic model was used to represent the powders. The relationship between the relative density of powder sample and applied pressure was predicted from finite element analysis and compared with the experimental data. A very good agreement between finite element results and experimental data was observed during the cold isostatic pressing.