Silylated waterborne polyurethane was synthesized by capping the NCO groups of polyurethane prepolymer, prepared from isophrone diisocyanate, poly(tetramethylene glycol) and dimethylol propionic acid, with aminopropyl triethoxysilane. Subsequently, it was mixed with colloidal silica to prepare silylated waterborne polyurethane/silica nanocomposites. The average sizes of nanocomposite particles, measured by dynamic light scattering, showed almost the same value, irrespective of increasing silica content. However, the prepared nanocomposites showed better thermal stability than pure waterborne polyurethane.