A series of co-precipitated silica-aluminum phosphate containing between 0 and 100 mol% silica were synthesized by a coprecipitation technique and characterized by various methods. X-ray fluorescence analysis shows that the P/Al molar ratio in the solid mixture decreases as the silica content increases, whereas this ratio remains one in the solution. Nearly all these materials are shown to be meso- and macroporous. The specific surface area decreases with increasing aluminum phosphate content, whereas the pore volume passes through a maximum at high silica content. Al-27, P-31, and Si-29 MAS-NMR spectra have also shown the existence of domains of silica and aluminum phosphate in binary supports, but these domains are not larger than a few microns, as shown by EDS measurements.