Magnetic nanocomposites of Co-ferrite nanoparticles dispersed in silica matrix (CoFe2O4/SiO2) have been prepared by the sol–gel technique using tetraethylorthosilicate (TEOS) as precursor of silica, and metallic nitrates as precursors of ferrite. Samples prepared in powder form have been dried at 100 °C for 3 h and calcined for 2 h at temperatures between 500 and 1000 °C. Co-ferrite particles were formed in the matrix pores and the nucleation of these particles was observed with the increase in the calcining temperature. TEM measurements showed that the nanoparticles had a fairly uniform morphology and an average particle size of approximately 5 nm. The combination of different Co-ferrite concentrations and calcining temperatures allowed to obtain samples with saturation magnetization ranging from 0.7 to 21.8 emu/g.