The electrostatic layer-by-layer assembly method was successfully used in a multilayer buildup of polyaniline (PANI) and platinum nanocrystals encapsulated in the carboxyl-terminated poly(amidoamine) dendrimers (generation 4.5 G4.5COOH) (Pt-G4.5COOH NPs) on solid substrates. Multilayer growth was monitored by ultraviolet–visible (UV–vis) absorption spectroscopy. The AFM observation revealed a molecularly smooth (PANI/Pt-G4.5COOH NPs) m multilayer film which is rougher and thicker than the multilayer of PANI and G4.5COOH (G4.5COOH/PANI) m . The PANI/Pt-G4.5COOH NPs multilayers show a fast surface-confined electron-exchange process at the Au electrode in an acid solution, and remains stable, reversible and electroactive, even in neutral solution. Furthermore, the multilayers show a strong electrocatalytic response towards CO oxidation and O2 reduction, and the catalytic capability can be easily tuned by the control of multilayer thickness.