Hyperbranched thin film (HTF) with amino and imino groups, which can accommodate PtCl62-, was synthesized with small organic molecules on gold substrate based on SN2 displacement reaction. Platinum nanoparticles (Pt-NPs) were in situ synthesized by electrochemically reduction of precursors, PtCl62-, within HTF. The prepared films were characterized by X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). It was confirmed that densely packed Pt-NPs were prepared with a narrow size distribution. EIS indicated that HTF inhibits electron transfer slightly while Pt nanoparticles in the HTF enhanced the electron-transfer ability greatly. Cyclic voltammetry (CV) indicated that HTF containing Pt-NPs exhibited a remarkable electrocatalytic activity for the electrochemical reduction of dioxygen. The quantity of Pt-NPs could be expediently controlled by the thickness of HTF. So the catalytic ability can be tailored correspondingly. (C) 2005 Elsevier Ltd. All rights reserved.