Mesostructured silica SBA-15 materials with different structural parameters, such as pore size, pore volume, and wall thickness, etc., were prepared by varying the postsynthesis hydrothermal treatment temperature and adding inorganic salts. The hydrothermal stabilities of these materials in steam (100% water vapor) were systematically investigated using a variety of techniques including powder X-ray diffraction, transmission electron microscopy, nitrogen sorption, and Si-29 solid-state NMR. The effect of the pore size, microporosity or mesoporosity, and wall thickness on the stability was discussed. The results show that all of the SBA-15 materials have a good hydrothermal stability under steam of 600 ° C for at least 24 h. N-2 sorption measurements show that the Brumauer-Emmett-Teller surface area of SBA-15 materials is decreased by about 62% after treatment under steam at 600 ° C for 24 h. The materials with thicker walls and more micropores show relatively better hydrothermal stability in steam of 600 ° C. Interestingly, we found that the microporosity of the mesostructured silica SBA-15 is a very important factor for the hydrothermal stability. To the materials with more micropores, the recombination of Si-O-Si bonds during the high-temperature steam treatment may not cause direct destruction to the wall structure. As a result, SBA-15 materials with more micropores show better stability in pure steam of 600 ° C. Nevertheless, these materials are easily destroyed in steam of 800 ° C for 6 h. Two methods to effectively improve the hydrothermal stability are introduced here: one is a high-temperature treatment, and another is a carbon-propping thermal treatment. Thermal treatment at 900 ° C can enhance the polymerization degree of &3bond; Si-O-Si&3bond; bonds and effectively improve the hydrothermal stability of these SBA-15 materials in 800 ° C steam for 12 h. But, this approach will cause very serious shrinkage of the mesopores, resulting in smaller pore diameter and low surface area. A carbon-propping thermal treating method was employed to enhance the polymerization of &3bond; Si-O-Si&3bond; bonds and minimize the serious shrinkage of mesopores at the same time. It was demonstrated to be an effective method that can greatly improve the hydrothermal stability of SBA-15 materials in 800 ° C steam for 12 h. Furthermore, the SBA-15 materials obtained by using the carbon-propping method possess larger pores and higher surface area after the steam treatment at 800 ° C compared to the materials from the direct thermal treatment method after the steam treatment.