The present study focuses on the structural properties of a NiO-SiO2 nanocomposite with 14 mol % of nickel oxide obtained by a sol-gel method and a gradual heating the gel in the 350-900 degreesC range. NiO nanoparticles and their dispersion in the amorphous silica matrix were studied through TEM and XRD. The behaviour at the nanoparticle/matrix interface was investigated through IR and Si-29 MAS NMR spectroscopy comparing the spectra of the nanocomposite with that of a silica sample obtained with the same preparation method and submitted to the same thermal treatments. The results indicate that nanoparticles, formed in cavities of the silica matrix, act as an obstacle towards the spontaneous silica polymerization process with heat treatments.