Mesoporous silicophosphates containing up to 22% phosphorus were prepared using cationic surfactants. A mesoporous silicophosphate of the approximate composition Si19P4O48 had a surface area of 770 m(2)g(-1), after removal of the template. A thermal transformation from a lamellar to a hexagonal structure was observed in this solid. The mesoporous silicophosphate phases were characterized by infrared and NMR spectroscopy.