The novel, magnesium-substituted tungstoarsenate, [As2W15Mg3O62](18-) (As2W15Mg3) (1) has been synthesized from the lacunary precursor [As2W15O56](12-) and characterized by elemental analysis, IR, UV and W-183 NMR spectroscopy. The W-183 NMR spectrum of 1 exhibits three lines of 1:2:2 intensity at -141.17, -147.86 and -183.02 ppm, as expected for the C-3v structure of the tri-substituted alpha-Dawson anion. The electrochemical behavior of 1 in aqueous solution has been investigated. The compound exhibits successive reduction processes of the W atoms in a negative potential range. The compound As2W15Mg3-containing monolayer and multilayer films have been fabricated on ITO substrate with poly(diallyldimethylammonium) chloride (PDDA) by layer-by-layer deposition. Thus-prepared multilayer films were characterized by cyclic voltammetry (CV), UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of the multilayer films shows three reversible two-electron redox waves in acidic aqueous solution in the potential range of 0.4 to -0.7 V, which are same with that in the solutions. The electrochromic behavior of the multilayer films has been studied in situ CV-UV-visible spectroelectrochemical methods, indicating the multilayer films show suitable response times and good reproducibility of response. This study provides a new compound to explore the possibility of application as electrochromism material. (C) 2008 Elsevier B.V. All rights reserved.