Pure silica mesoporous molecular sieves were synthesized from a fluorosilicon compound in which the cationic surfactant had been removed either by calcination or acidified solvent extraction at atmospheric pressure. The mesoporous materials prepared by direct calcination and extraction were heated up to 100 ℃ at a sample/water ratio of 1 g to 1000 mL during 12-24 h in order to investigate the hydrothermal stability. The change of structure caused by XRD, nitrogen adsorption/desorption, TEM, and TGA was measured. It was found that the material prepared by direct calcination maintained a mesopore structure after hydrothermal treatment for 12 h, however, this mesopore structure collapsed after hydrothermal treatment for 12 h due to hydrolysis in the Si-O-Si linkages. The samples prepared by the extraction process exhibited no significant change in their mesopore structure even after hydrothermal treatment for 18 h. In the case of the samples treated hydrothermally for 24 h, the pore size distributions showed a narrow uniform mesopore from 20 to 30 Å. However, the pore structure of the samples was less uniform than that of the non-treated samples. Accordingly, it can be concluded that materials prepared by extracting the surfactant with organic solvents have more hydrothermal stability than materials prepared by direct calcination. These results can be explained by an increase in the wall thickness, and decrease of the silanol group in the mesopore structure.