Novel nanocomposites of barium hexaferrite- and fullerene-containing polyurethane were synthesized and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and energy-dispersive X-ray diffraction. The nanoparticles showed good dispersion in the polyurethane matrix. Their thermal, mechanical, and electromagnetic absorbance properties were studied. The complex permeability and permittivity were measured in the frequency range of 8.2-12.4 GHz. The maximum reflection loss of the nanocomposites was found to increase with increasing the ferrite content from 1% to 5%, with maximum value of -7.5 dB at only 5% composition. The incorporation of nanofiller not only imparts mechanical strength to the nanocomposite but also shows good radar-absorbing properties at only 5% filler concentration. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3204-3211, 2011