Four silica-zirconia composites were prepared using a sol-gel process and compared with zirconia, which was prepared under the same conditions but without the addition of sodium metasilicate pentahydrate. Spherical particles (1-2 mu m) resulted which were free from aggregation and hollow spheres. Raman spectroscopy, differential thermal analysis, thermal gravimetric analysis and electron microscopy were used to evaluate the properties of these composites. Addition of the silica onto the zirconia microspheres prevented the formation of monoclinic zirconia and increased the temperature of crystallization into the tetragonal form. Calcination of the composites at 1300 degrees C produced zircon.