Novel poly(butylene terephthalate) (PBT)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized by ring-opening polymerization of cyclic poly(butylene terephthalate) initiated by functionalized POSS with various feed ratios. The impact of PUSS incorporation on melting and crystallization behaviors of PBT/POSS nanocomposites was investigated by means of X-ray diffraction and differential scanning calorimetry. It was found that the novel organic-inorganic association result in the significant alterations in the melting and crystallization behavior of PBT. Thermal studies confirmed that the incorporation of POSS can enhance the thermal stability of the polymers, and the copolymer glass transition temperature increased with the increasing of POSS macromonomer content. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1853-1859, 2010