Surface-modified colloidal silica (M-CS) nanoparticles were successfully synthesized from colloidal silica (CS) and methyltrimethoxysilane using sol-gel method and characterized by Fourier transform-infrared spectroscopy. Both CS and M-CS were then incorporated into acrylic adhesives. M-CS particles in 2-ethoxyethanol had similar particle size to pure CS based on the characterization by DLS. The morphologies of M-CS particles in acrylic adhesives examined by TEM showed more homogeneous dispersities than that of pure CS which were aggregated and phase separated in acrylic adhesives. In addition, the thermal properties of the nanocomposite acrylic adhesives determined by thermogravimetric analyses and differential scanning calorimetry showed higher glass transition temperature and thermal properties than pure acrylic adhesives. Finally, the 180 degrees peel strength of nanocomposite acrylic adhesives was higher than pure adhesives with improved durabilities.