This Book is containing the synthesis and characterization of hydrophobic silica nanoparticles using sol gel process. Different modifiers (alumina sol, zirconium sol, titanium sol and hexameythyl disilizane) were added to silica with different percentage to convert silica to hydrophobic materials. The effects of these modifiers on the texture and characteristics of silica nanoparticles were investigated using different techniques such as FESEM, TEM, FTIR, XRF, XRD, TGA and BET.