The PANI/Pd-0 nanocomposite films with Pd nanoparticles embedded in the polyaniline (PANI), were successfully fabricated through the simple layer-by-layer (LBL) adsorption of PANI and PdCl62-, followed by the in situ electrochemical reduction of the incorporated PdCl62- in the multilayer film. The as-prepared composite films were characterized by X-ray photoelectron spectroscopy, UV-vis spectroscopy, Fourier-transform infrared, atomic force microscope and transmission electron microscopy. The size of Pd nanoparticles in the composite film could be fine-tuned in the range of about 2-22 nm by varying the concentration of PdCl62-. PANI in the nano-structured PANI/Pd-0 composite films still shows the good redox activity in neutral pH solution. The as-obtained PANI/Pd-0 nanocomposite film presents an excellent electrocatalytic activity to hydrazine oxidation. And the catalytic performance is not only dependent on film thickness, but also Pd-0 size. On the 5-bilayer PANI/Pd-0 film with Pd-0 particles 2 nm in size, two calibration curves were found in the concentration ranges of 3.0 x 10(-7)-3.5 x 10(-4) M and 5.0 x 10(-4)-1.2 x 10(-2) M. And the minimal detectable concentration was down to 5.0 x 10(-8) M on the electrode with 13 bilayers buildup. The substrate can be used repeatedly for consecutive detection of hydrazine with good stability. (C) 2012 Elsevier Ltd. All rights reserved.