We report an efficient and simple method to synthesize tungsten oxide nanostructures, including high quality and quantity nanowires, through thermal evaporation of WO₃ powders without catalyst. The thermal evaporation processing was conducted in a three zone horizontal tube furnace over temperatures ranging from 300 to 800℃, where multiple substrates were placed at different temperature zones to form distinct nanostructures, such as films, nanorods and nanowires. The temperature of each zone was measured by a thermal couple. Processing parameters, including pressure, temperature, type of gas and flow rate, were varied and studied in terms of their influence on the morphology, aspect ratio and density of the nanowires. The morphologies of the products were observed with scanning electron microscopy. High resolution transmission electron microscopy and x-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanostructures. Additionally, the growth mechanism has been proposed. Furthermore, we investigated the doping effect on physical properties of the nanostructures. Since tungsten oxide has lots of interesting properties, including chromism, optical and field emission, the research at nanoscale here supports the development of promising potential applications for sensors, light-emitting diodes and field emitters.