In the last few years much progress has been made in the development of hybrid polymer-inorganic filler nanocomposites. Nevertheless, many questions remain. The comprehension of the structure and the interactions at the polymer-nanofiller interface are crucial to foresee and control the properties of nanocomposites. Because of the high surface ratio of the inorganic nanofiller, the interface is expected to have a prevailing role in determining the nanocomposite properties. In this study we use X-ray photoelectron spectroscopy (XPS) as a tool for the surface characterization of an organophilic montmorillonite/poly(epsilon-caprolactone) exfoliated nanocomposite. The XPS core levels of the nanocomposite have been compared with those obtained from its precursors, and analyzed as reference compounds to evaluate eventual differences attributable to the polymer-nanofiller interfacial interactions. The XPS investigation has allowed us to propose a qualitative model of possible interface interactions between poly(epsilon-caprolactone) and the organo-modified montmorillonite. The model is substantiated by Fourier transform infrared spectroscopy (FTIR). (C) 2004 Wiley Periodicals, Inc.