This article describes the thermal properties of clay-containing poly(ethylene succinate) (PES) nanocomposite. The nanocomposite of PES with organically modified montmorillonite (o-mmt) has been prepared by solution-intercalation-film-casting technique. Small-angle X-ray scattering patterns and transmission electron microscopy observations show the homogeneous dispersion of silicate layers in the PES matrix. The crystallization and melting behaviors of the PES matrix in the presence of dispersed silicate layers have been studied by differential scanning calorimeter, polarized optical microscope, and wide-angle X-ray scattering. Results show that the incorporation of o-mmt stops the super-cooling effect and accelerates the mechanism of nucleation and crystal growth of PES matrix significantly. The incorporation of o-mmt also improves the thermal stability of neat PES dramatically. (C) 2009 Elsevier Ltd. All rights reserved.