A novel method, a hydrothermal method, was firstly employed to prepare a catalyst of Pt supported on carbon nanotubes (Pt/CNTs) used in a proton exchange membrane fuel cell (PEMFC) in the present work. The catalyst was characterized through the IR spectrum, XRD, TEM and Image-Pro PLUS2 software. The results show that the pretreatment using a HNO3-H2O2 redox system on CNTs opened the ports and removed a large quantity of impurities. Reaction temperature and time are important factors to determine the Pt granule size. The average size of the Pt nanoparticles is less than 1.94 nm with homogenous dispersion and narrow distribution under the optimal reaction conditions with a reaction time of 1.5 h at 140 degrees C. The hydrothermal method using the conventional Pt precursor H2PtCI6-2H2O together with HCHO with brief operation will be a promising method to yield Pt nanoparticles for the Pt/CNTs catalyst. (c) 2006 Elsevier Ltd. All rights reserved.