Exfoliated poly(ethylene terephthalate) (PET)-layered silicate nanocomposites (P(et)LSNs) excluding (PetLSNeom) and including (PetLSNiom) organic modifiers were obtained by solution methods with and without solvent-nonsolvent system, respectively. From wide angle X-ray diffraction and high resolution transmission electron microscopy, both P(et)LSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in PetLSNiom was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in PetLSNiom. Thus, the effect of the presence and absence of organic modifiers in P(et)LSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both P(et)LSNs had higher degrees of crystallinity and shorter crystallization half-times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both P(et)LSNs. However, PetLSNiom exhibited a lower degree of crystallinity and longer half-time of crystallization than PetLSNeom. Difference of crystallization behavior between PetLSNiom and PetLSNiom was ascribed to organic modifier in PetLSNiom, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. (c) 2008 Wiley Periodicals, Inc.