The effect of a foreign substance, silica (SiO2), on the surface chemistry, chemical reactivity, and dispersibility of titania (TiO2) nanoparticles was investigated. SiO2 covers 90% of the surface of commercially available TiO2 nanoparticles and provides higher acidity, which facilitates the absorption of alkaline surfactant, oleylamine, onto TiO2 nanoparticles, leading to more efficient nanoparticle dispersion. By removing the surface SiO2 with an acid treatment, the acidity of TiO2 was highly reduced and became favorable to being adsorbed and dispersed by the acidic surfactant, oleic acid.