Crystalline WO3 nanorods of less than 100 nm in diameter have been successfully synthesized at 240 °C for 72.0 h with pH=1.5 in the system of strong acid with sodium tungstate and potassium sulphate by the hydrothernal method. The morphologies and structures of WO3 rods have been characterized and analyzed by XRD, SEM, TEM and SAED. SEM confirmed that the slenderness ratio of WO3 rods was enlarged with the increase of t the pH value and the reaction time. SAED analysis showed that the crystal morphology of the synthesiezed WO3 nanorods was crystallin. UV-VIS results showed that the absorbent power of UV light for WO3 nanorods enhanced with the increase of their slenderness ratio.