Hyperbranched thin film (HTF) with amino and imino groups, which can accommodate PtCl6 2−, was synthesized with small organic molecules on gold substrate based on SN2 displacement reaction. Platinum nanoparticles (PtNPs) were in situ synthesized by electrochemically reduction of precursors, PtCl6 2−, 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 PtNPs 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 PtNPs exhibited a remarkable electrocatalytic activity for the electrochemical reduction of dioxygen. The quantity of PtNPs could be expediently controlled by the thickness of HTF. So the catalytic ability can be tailored correspondingly.