The effect of morphology of iron powders on their compaction behaviour has been studied in the case of compacts with a final relative density below 0.8. Two powders, one with spherical grains and the other with spongy grains, have been synthetized in order to prepare green compacts under pressures ranging from 100 to 350 MPa. The compaction behaviour of both powders has been experimentally described by the relation between the applied compaction pressure and the relative density of the material. Different stages have been identified at increasing compaction pressure: (i) fully elastic behaviour (Stage I), (ii) particle sliding (Stage II), (iii) particle irreversible deformation (Stage III). Spongy powder-based compacts achieved greater density at the same compaction pressure than spherical powder-based compacts, Models are proposed to describe the compaction behaviour of both powders.