X-ray Photoelectron Spectroscopy (XPS) is commonly used to study the chemical composition of TiC/C nanocomposite films. Nevertheless, XPS remains a surface analysis technique and the obtained chemical information can be strongly affected by the surface oxidation and carbon contamination of the nanocomposite samples due to their exposure to air. Generally, an erosion stage is performed before XPS analysis using argon ion bombardment to remove the surface contamination. Since ion bombardment is likely to modify the surface chemical composition of the films, the question of whether XPS results are really representative of the bulk nanocomposite material can be addressed. Therefore, this study is devoted to the effect of ion bombardment on the surface chemical composition of nanocomposite films. TiCx and TiCxOy films were grown by a hybrid plasma process combining Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition. Then, the samples were transferred to the XPS system where an in situ study of the modification of the surface chemical composition under argon ion bombardment was performed. XPS results are compared to Energy Dispersive X-ray analysis. (C) 2011 Elsevier B.V. All rights reserved.