Epoxy matrix composites have been prepared using as filler different weight fractions (0.03-1 wt%) of CVD grown multi-walled carbon nanotubes (MWCNTs) containing trapped iron nanoparticles. Magnetic characterization performed at room temperature with magnetic field between - 19 and 19 kG shows that the nanocomposites are weakly ferromagnetic at room temperature. An abrupt variation in the dependence of both the coercivity field, B-C, and remanent magnetization, M-R, with the weight fraction of MWCNTs, phi, was found for phi = 0.4%. Results suggest the formation of MWCNTs agglomerates for increasing weight concentrations, in accordance with SEM micrographs. (c) 2005 Elsevier Ltd. All rights reserved.