Fe2O3 nanoparticles were formed within SiO2 framework via a sol-gel co-precipitation synthesis route. Various weight percentages of Fe2O3 in the composites ranging from 8.6 to 52.8 wt.% were formulated. X-ray diffraction and Raman spectra indicated the formation of alpha-phase Fe2O3 nanoparticles. EPR spectra of the Fe2O3 nanocomposites were found to depend significantly on the weight composition of Fe2O3. The composite with a sufficiently large amount of Fe2O3 was found to show a nonzero absorption at zero-applied field, which indicates the partial alignment of magnetic dipole moments within the composites. From Q factor measurements we further found that such sufficiently loaded composites show substantial microwave absorption capability. (c) 2005 Elsevier B.V. All rights reserved.