Sol-gel aluminosilicate glasses containing 1 mol% of Fe2O3 and different amounts of Al2O3 (1; 2; 3; 4; 6 and 8 mol%) have been investigated. The ultraviolet-visible-near infrared spectrophotometry (UV-VIS-NIR), electron paramagnetic resonance (EPR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), has been employed to obtain information about the structural evolution of the samples. The concentration of Al2O3, the treatment temperature and the furnace atmosphere play an important role in the structural incorporation of iron. The treatment of the samples, in air and under reducing conditions, results in remarkable changes in the UV-VIS-NIR and EPR spectra. In the samples were detected nanoparticles. The low temperature blocking of the nanoparticles magnetic moments has been clearly evidenced in the EPR derivative spectra at low temperatures.