Polymer/inorganic nanocomposites were significant hybrid materials because of their unique properties. The surface of bare nanoparticles (b-TiO2) was modified by aminopropyl trimethoxy silane to obtain grafted TiO2 (g-TiO2) nanoparticles for the improvement of nanoparticles dispersion. The b-TiO2 and resulting g-TiO2 nanoparticles were introduced into poly(e-caprolactone) (PCL) matrix to prepare PCL/TiO2 nanocomposites by in situ polymerization. The effects of b-TiO2 and g-TiO2 nanoparticles on the structure, morphology, and properties of nanocomposites were characterized and compared. The results showed that the crystalline structure of PCL matrix was not affected significantly by adding b-TiO2 or g-TiO2 nanoparticles. The g-TiO2 nanoparticles had a finer dispersion and better compatibility than bare TiO2. The introduction of g-TiO2 into PCL matrix increased the crystallization temperature and improved thermal stability of the nanocomposites with respect to untreated TiO2. The surface-treated nanoparticles played an important role in strengthening mechanical properties of the nanocomposites because of its well dispersion and strong interfacial interaction between the nanoparticles and PCL matrix. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012