This paper reports the analysis of 4-mercaptoaniline (p-HSC6H4NH2) functionalized platinum nanoparticles by X-ray photoelectron spectroscopy (XPS). The spectra are recorded on mixed Langmuir-Blodgett (LB) films containing fatty acid and platinum particles in proportion 50/50. The LB films are deposited on gold layer made by thermal evaporation on glass substrate. The quite good stability of the nanomaterial under X-ray exposure is reported from one minute to two hours thirty. A line profile is conducted on seventeen points of a LB film to check the good homogeneity of the deposition. The elemental composition of the nanoparticule core-shell structure is reported for platinum sulfur and nitrogen. Then, the evolution of the Pt 4f core level intensity compared to the An 4f signal coming from the burried gold electrode is established as a function of film thickness. From this analysis the effective electron attenuation length of Pt 4f photoelectrons and the effective value of platinum atom density are determined. Further exploitation of these data leads to an averaged interparticle distance in the nanocomposite. Comparison of these results with those recorded from X-rays reveals a quite good aggreement and validates the XPS intensities treatment. (C) 2004 Elsevier B.V. All rights reserved.