Nanocomposites with cobalt ferrite nanoparticles uniformly dispersed in silica have been successfully synthesized. The effects of the thermal treatment temperature and the initial drying temperature on the structural and magnetic properties of the nanocomposites were examined. The crystalline phase, the particle size, and the homogeneity of the resulting nanocomposites were studied by X-ray diffraction, IR spectroscopy, differential scanning calorimetry, transmission electron spectroscopy and vibrating sample magnetometer. The xerogels were amorphous. Heat treatment at 400 degreesC resulted in CoFe2O4 clusters being partially formed and when the heat treatment temperature was increased to 600 degreesC, CoFe2O4 clusters were formed in large quantities. The formation reaction of CoFe2O4 clusters was accompanied by a rearrangement of the silica matrix network. On further increasing the heat treatment temperature to 800 degreesC, materials with CoFe2O4 nanocrystals, well crystalline dispersed in the silica matrix, could be obtained. By increasing the annealing temperature, composites with a progressive increase of the coercivity and of the remanent magnetization were produced. The remarkable effect of initial drying temperature on the particle size of cobalt ferrite suggested that a well-established silica network provided an effective confinement to the coarsening and aggregation of CoFe2O4 nanoparticles. (C) 2004 Elsevier B.V. All rights reserved.