Herein, efficient amino modification of silica (SiO2) nanoparticles using tris(hydroxymethyl)aminomethane (Tris) was performed via aqueous mixing, spray drying, and thermal treatment. The hydroxymethyl and amino groups of Tris reacted with the silanol groups on the SiO2 particle surface. Tris amination does not produce volatile organic compounds. Moreover, Tris does not condense itself and can be easily grafted in a single molecular layer on the particle surface. The grafting density of Tris reached 2.60 nm(-2). Tris amination increases the reactivity of the particle surface and significantly enhances the grafting density of stearic acid on the SiO2 particles and the hydrophobicity of the particles.