WO3−x nanorods were grown on the tips of electrochemical etched W filaments by in-situ heating under different growth conditions. This kind of nanorods has the average diameter of 20 nm and the length of 1–2 μm. Transmission-electron microscopy investigations indicate that the sub-stoichiometric WO3 nanorods, prepared at about 830 °C under the atmosphere of H2 and Ar mixture, could grow along the either 〈0 0 1〉 or 〈1 1 0〉 direction with evident stacking faults and textural structure. Nanorods prepared without H2 atmosphere are found to be respectively W18O49 grown at around 900 °C and WO2.9 grown at 800 °C.