Hydrophobic silicas were prepared as follows: 0.5g of silica powder was dried at 200°C in an electric furnace and then the powder was treated in n-hexane solution containing 1.0g of 2, 4-tolylenediisocyanate (2, 4-TDI) at room temperature for 4h. The other isocyanates, hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), methylene diphenylisocyanate (MDI) and phenyl isocyanate (PI) were used. Surface modification by IPDI and MDI gave hydrophobic silica. The conditions for preparing hydrophobic silica, such as drying temperature and reaction time were investigated. Also the dispersibility of the products to some organic solvents was discussed.