Self-assembled films from SnO2 and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer (LbL) method. The modified electrodes were immersed into a H2PtCl6 solution, a current of 100μA was applied, and different electrodeposition times were used. The SnO2/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5molL−1 H2SO4, at a sweeping rate of 50mVs−1. Oxygen-like species are formed at less positive potentials for the Pt–SnO2/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300kΩcm2) compared with the Pt–SnO2/PAH film with 1min of electrodeposition (0.4kΩcm2). According to the Langmuir–Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt–SnO2/PAH concerning ethanol electrooxidation. With these features, this Pt–SnO2/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC).