In this paper, a new method of fabricating multilayers on a carbon substrate is presented. First, a uniformly charged carbon surface was prepared through molecular design. Then an ultrathin film consisting of layer-pairs of oppositely charged polymeric cationic poly(diallyldimethylammonium chloride) (PDDA) and silicotungstate, SiW₁₂O₄₀⁴⁻ (SiW₁₂), was grown layer-by-layer onto the grafted carbon substrate using a molecular self-assembly technique and an electrochemical method. The technique allows one to prepare highly adherent, dense and smooth films of polyoxometalates with special properties. By combining cyclic voltammetry (CV) and X-ray (XR) reflectometry, it was determined that the average surface density of SiW₁₂ was 2.10 × 10⁻¹⁰ mol cm⁻², and the thickness increase per adsorption of PDDA–SiW₁₂ was 1.7 ± 0.2 nm, indicating that the amount of SiW₁₂ anion per one layer adsorption corresponded to a monolayer coverage. Atomic force microscopy (AFM) was also used to examine the surface morphology and determine the grain size distribution and roughness for multilayer films. An increase in root-mean-square (RMS) surface roughness from 7 to 9 Å was observed as the number of layer-pairs in the film increased from 2 to 6. FTIR results showed that the good stability of the multilayer films was due to Coulomb interactions between the SiW₁₂ anion and the polymeric cations PDDA. Moreover, the multilayer films, in acidic aqueous solution, showed good electrocatalytic activity toward the reduction of NO₂⁻, and the catalytic currents increased with increasing the layer numbers of SiW₁₂ adsorption. These characteristics of the multilayer films might find potential applications in the field of sensors and microelectronics devices.