A novel nanosized multilayer film containing polyoxometalate anion with a pendant supportligand α-[SiW11O39Co(H3P2O7)]7- (abbr. SiW11Co-P2O7) and poly(diallyldimethyl ammonium chloride (PDDA) was fabricated by layer-by-layer self-assembly. The multilayer film was characterized by XPS, UV-vis, AFM and ESR. The mean interface roughness was about 2.0 nm, calculated from an area of 0.5 × 0.5 μm2. The electrochemical property was studied by the cyclic voltammetry, the results indicating that the self-assembly film exhibited favorable electrochemical behavior of polyoxometalate.