An easy method to synthesize Pt nanoparticles supported on conductive polymers has been explored. The synthesis was carried out under “soft” conditions, i.e., at low temperatures and without using strong reducing agent. The optimal synthesis conditions have been established. Thus, the particles had almost monodisperse size distribution, around 2.4 nm, when the synthesis was carried out at 100 °C, and around 1.4 nm when it was done at 75 °C. Also, it has been demonstrated that the platinum loading and the pretreatment of the catalyst determine the catalyst activity. Cyclic voltammetry in sulfuric acid displayed the processes of adsorption−desorption of hydrogen. The PANI−Pt catalysts have been checked in the oxidation of methanol, and a low degree of poisoning due to carbon monoxide adsorption has been detected in comparison with bulk platinum. ; Financial support by the Ministerio de Educación y Ciencia (Granrt MAT2004-1479) and the FEDER funds. H.J.S. thanks the Ministerio de Educación y Ciencia of Spain for a Juan de la Cierva Contract. C.S thanks the MEC for a FPU fellowship.