The compaction behavior of structure-modified Fe nanopowders having agglomerates of spherical shape and a bimodal particle size distribution was investigated in terms of the particle packing and microstructure during compaction process. To fabricate the structure-modified Fe nanopowders, the spray-dried Fe2O3 nanopowder was hydrogen reduced at 400, 450 and 550 degrees C to control the degree of particle growth in agglomerates. The compaction behavior of fabricated Fe nanopowders was investigated by two different ways. In die compaction experiments, it was found that the bimodal nanopowder reduced at 550 degrees C showed higher green density compared to nanopowders reduced at 400 and 450 degrees C over the entire range of compacting pressure. Furthermore, the compact of the bimodal nanopowder achieved a remarkable green density over 80% of theoretical density (TD) at 1000 MPa pressure without any defects due to the effective packing by filling the interstices between the large nanoparticles with small nanoparticles. The obtained density-pressure data was fitted by the Panelli and Ambrozio Filho equation to compare the densification capacity between the fabricated Fe nanopowders. To investigate the agglomerate deformation occurrence at the low pressure range, a continuous compaction experiment was conducted; the observations were explained in terms of microstructural development on the basis of the apparent yield pressure obtained from continuous densification curves. (C) 2018 Elsevier B.V. All rights reserved.