This paper reports on the study of the evolution of 4-mercaptoaniline (p-HSC6H4NH2) functionalized platinum nanoparticles in solution by coupling the Langmuir-Blodgett technique and X-ray photoelectron spectroscopy (XPS). The spectra are recorded on mixed LB films containing fatty acid and platinum particles in proportion 50/50. Several samples built from fresh and aged solutions of particles are analyzed. Comparison of the Pt 4f, S 2p and N 1s regions in each case points to the time dependant chemical evolution of the functionalized particles involving at once platinum, thiolate and amine components. The particle aging in solution is reported during several months, until the complete flocculation of the functionalized platinum nanoparticles. Using the compared XPS analysis of the LB layers obtained from the different particle solutions, unstability of the storage looks then clearly related to the chemical evolution of the bifunctional organic crown. (c) 2005 Elsevier B.V. All rights reserved.