Tungsten oxide nanostructured rods, particles and occasionally tubes are deposited by heating a tungsten filament in a partial oxygen atmosphere. Transmission electron microscopy (TEM) reveals the nanorods have similar to 10-50 nm diameters and similar to 50-200 nm lengths. The nanoparticle size ranges from similar to 10 to 200 nm. The nanostructures are generally crystalline and predominantly consist of the WO3 monoclinic (I) gamma-phase with some monoclinic (II) epsilon-phase and/or tungsten metal present. Under optimal synthesis conditions, only crystalline nanostructures with a largest dimension of similar to 200 nm are observed with TEM analyses. Further characterization conclusively shows that these 'optimal' nanostructures are comprised of only the WO3 monoclinic (I) gamma-phase. (c) 2005 Elsevier B.V. All rights reserved.