UV-Visible, NIR and Raman spectroelectrochemistry techniques have been used for the in-situ study of Pt nanoparticles (PtNPs) electrosynthesis on an electrochemically generated poly(3,4-ethylenedioxythiophene) film. Two electrochemical steps have been used to obtain in a reproducible way PtNPs with catalytic properties towards methanol oxidation: 1) deposition of Pt nuclei on the polymer modified electrode, 2) growth of these nuclei to form nanoparticles yielding drastic changes in the spectroscopic signal and a significant increase of the amount of Pt. A two steps procedure facilitates an interfacial growth mechanism of the nuclei over a diffusion controlled growth. Evolution of UV-Visible and NIR spectra during these two PtNPs synthesis steps helps to understand and explain the mechanism of generation of these nanoparticles. Besides, Energy Dispersive X-Ray analysis and Scanning Electron Microscopy images registered of the composite after each step of synthesis confirm the conclusions extracted from spectroelectrochemistry data. (C) 2014 Elsevier Ltd. All rights reserved.