The adsorption of bis-[3-(triethoxysilyl)propyl]tetrasulfide (Si-69) coupling agent onto fumed silica is affected by the solvent polarity and the silane concentration. Chemisorbed silane onto silica studied by quantitative FTIR reveals that polar solvents, especially water and ethanol, yield significantly more chemisorbed silane than non-polar solvents. In contrast, physisorbed silane is dominant in non-polar solvents. In the case of silane concentration effect, the chemisorbed silane increases with silane concentration until the saturation point. By varying silane concentration, physisorbed silane in both polar and non-polar solvents is found to increase as the silane concentration increases.