The effects of the surface silanol structure and interaction force between solid surfaces in water on the gel structure using acid catalyzed hydrolysis alkoxide-derived silica gels with various preparation conditions. The present study focused on the amount of catalysts and H2O/TEOS mole ratios. Surface silanol structure, interaction between solid surfaces and the structure in dried-gels were determined by a FT-nIR, FT-IR, Atomic Force Microscope (AFM) and a mercury porosimetry, respectively. As results, when a relatively low H2O/TEOS mole ratio ( from 4 to 40) was used, surface silanol was almost hydrogen bonded silanol, and isolated silanol disappeared. Since this hydrogen-bonded silanol formed a hydrogen bonded water layer on silica surface, short-range additional hydration force (less than 2 nm) appeared between solid surface and the tip of AFM. When H2O/TEOS mole ratio increase in the range from 20 to 40, the surface density of isolated silanol increased and that of residual Si-OC2H5 decreased. Relatively long-range additional repulsive force on these silica gels reached 20 nm from solid surface. The pore diameter in each dried gel almost corresponded to the surface distance, which acted the additional repulsive force.