SiO2 aerogel has been investigated for the application of interlayer dielectrics (ILD) in microelectronics. Its lowest permittivity originated in its inherent porous structure among various candidate materials makes it applicable to the ULSI devices. However, because of its high porosity and large surface area, moisture adsorption occurred after fabrication of SiO2 aerogel film. A number of OH groups due to incomplete condensation reaction induce moisture adsorption through hydrogen bonding. This hydrophilic characteristic of hydroxyl group obstructs its application to ILD. Besides, dipole moment of OH group is higher than alkyl or alkoxy group. So it is inferred that replacement of this hydroxyl group with hydrophobic alkyl group lowers the dielectric constant of aerogel. In this research, silylation agent such as trimethylchlorosilane (TMCS) was used to remove hydroxyl group and protect aerogel surface.