The properties of porous SiO2 xerogel film strongly depend on the aging process. The morphology of the surface modified SiO2 xerogel film pre-aged for 1 hr at 70 degreesC showed a two-dimensional structure. Aging for 12 h at 70 degreesC and successive modification of the film induced some particle growth and a three-dimensional network structure. The microstructure of the modified SiO2 xerogel films reflects the preformed structure during aging. The surface modification induced the changes of surface coverage from -OC2H5 and -OH bonds to -CH3. However the content of surface chemical species was almost same regardless of aging lime. The porosity of the modified sample pre-aged for 12 h at 70 degreesC was 89%. The calculated/measured dielectric constants were 1.31/1.42, respectively