Silica has been modified with decyltrimethoxysilane at various temperatures to improve the dispersion of the silica particles in a silica-rubber composite. The modified silica samples are characterized by FT-IR and Si-29 CP/MAS NMR. With increasing treatment temperature, the chemical reaction between the silanol group of silica and the methoxy group of decyltrimethoxysilane is facilitated and the silica samples demonstrate very low water vapor adsorption capacities and good hydrophobicity compared to silica. The SBR rubber composite containing thermally modified silica shows improved silica particle dispersion. However, when physically mixed silica is used, the silica is mainly located on the surface and agglomerated.