Magnetic nanocomposites formed by iron oxide particles hosted in silica aerogels pores have been synthesized by sol-gel processes and supercritical evacuation of the solvent. Two iron-containing salts have been essayed: (A) Fe(NO3) · 9H2O and (B) FeNa(EDTA) · 2H2O. The synthetic routes made use of the gel pores as nanoreactors. Structural and magnetic properties have been studied by combining X-ray diffraction (XRD), N2 adsorption isotherms, transmission electron microscopy (TEM), 57Fe Mössbauer spectroscopy and vibrating sample magnetometry (VSM). The nanocomposites properties, i.e., phase of the iron oxide, monolithic integrity, particle size distribution and magnetic phase dilution vary with the chosen synthetic path. The use of EDTA complex as a nanoparticle precursor increases the average pore diameter of the matrix. The nanocomposites are good candidates for applications in the field of magneto-optical sensors and magnetic devices due to their attractive properties, including soft magnetic behavior, low-density and electric resistivity. © 2001 Elsevier Science B.V.