In the present work the synthesis and characterization of nanophase metallic systems of Fe and Co stabilized with different matrices: silica mesoporous molecular sieves with ordered and disordered channels and polyvinyl pyrrolidone (PVP) polymer were studied. The metallic nanophases were introduced in the disordered channels mesoporous material by direct synthesis, at different pH (5 and 7) and by impregnation. For the ordered mesoporous material (MCM-41) only the impregnation method was carried out. The nanophase metallic particles onto PVP were prepared by salt reduction method. These systems were characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopic (EDS), X-ray diffraction (XRD), superficial area (BET), X-ray photoelectron spectroscopic (XPS) and electron paramagnetic resonance (EPR). A dependence of the particle size with the synthesis method was found. (c) 2005 Elsevier B.V. All rights reserved.