A Dawson type polyoxometalate K7P2W17O61(FeOH2)center dot 8H(2)O (P2W17Fe) and palladium nanoparticles (PdNPs) was used to construct a electrochemical sensing film. The composite film was fabricated by alternately depositing PdNPs and P2W17Fe on quartz and ITO substrates using the layer-by-layer method (LBL). The composite film was characterized by UV-visible spectrum. X-ray photoelectron spectrum and atomic force microscope. Cyclic voltammetry and amperometry were employed to explore the composite film's electrochemical properties and performance in sensing and detection. The results indicated that the composite film has good electrocatalytic activity towards the reduction of hydrogen peroxide and oxidation of hydrazine sulfate, and is capable of sensing H2O2 and N2H4SO4 at suitable potential. The detection limit, sensitivity and linear concentration range are 1 mu M (S/N = 3), 66.7 mu A mM(-1), 1.5 mu M to 3.9 mM for hydrogen peroxide and 1.5 mu M (S/N = 3), 0.24 mu A mM(-1), 2 mu M to 3.4 mM for hydrazine sulfate, respectively. The small Michaelis-Menten constant K-M of PdNPs-containing film compared to PdNPs-free film indicated that introduction of PdNPs enhanced effectively the electrocatalytic ability of the composite film. (C) 2012 Elsevier Ltd. All rights reserved.