Lenticular W18O49 nanobundles composed of ultra-thin nanowires with diameters of 5-10nm have been synthesized through a simple solvothermal method with hexachloride as precursor and mixed cyclohexanol and ethanol as solvent. Electrochromic films were prepared by assembling the W18O49 nanobundle suspension onto tin-doped indium oxide (ITO) coated glass. Results showed that self-assembly of the W18O49 nanobundles was strongly influenced by the solvents employed to disperse the nanobundles. The W18O49 nanobundles coated films exhibited excellent electrochromic stability and reversibility. The W18O49 nanobundle films also showed much higher charge-insertion density compared with the WO3 nanorod film, which may be due to the ultrathin feature of single nanowires constituting the nanobundles, unique oxygen vacancies of monoclinic W18O49, and the highly ordered assembly of the nanobundles. (C) 2011 Elsevier B. V. All rights reserved.