Abstract：Mesoporous silica film was successfully prepared through molecular self-assembly. A precursor sol containing tetraethoxysilane (TEOS), the surfactant template cetyltrimethylammonium bromide (CTAB) and acid catalyst was prepared by sol-gel process. The hexagonal ordered structure of the calcined mesoporous silica film was confirmed by TEM. The refractive index of the directly calcined film is 1.18, the film thickness is about 180 nm, which was performed by spectroscopic ellipsometry measurements. The dielectric constant k of the directly calcined film was 2.14. The hexamethydisilazane (HMDS) vapor treatment is considered to be effective possibly for generating hydrophobic mesoporous silica thin film, and the resulting film will be more useful as low dielectric constant intermetal material in advanced semiconductor devices.