The catalytic activity and thermal stability of lipase entrapped in organically modified silicates by the sol-gel method have been studied in ester synthesis in organic solvents. When methyltrimethoxysilane (MTrMOS) was used as the organic silane precursor which was mixed with tetramethoxysilane (TMOS) at a molar ratio of 3 : 1, the entrapped Lipase exhibited a higher esterification activity than the lipase deposited on Celite 545 at temperatures as high as 65 degrees C. This esterification activity was further enhanced by forming the lipase-entrapping gel on the surface of Celite 545. Thermal stabilization of lipase by entrapment in hybrid gels seems to be closely related to the mechanism of the sol-gel transition accompanied by microscopic phase separation. As a result of screening of different organic silanes, and of optimization of the preparation conditions, the hybrid gel-entrapped lipases on Celite 545 derived from an equimolar mixture of either propyltrimethoxysilane or trimethylmethoxysilane and TMOS were found to be the most thermostable, retaining their full activities up to 75 degrees C, and 100 to 200 times higher activity at 95 degrees C compared to the lipase deposited on the same support.