In this paper, a one-pot synthesis of WO₃ hollow sphere nanostructure has been realized via a one-pot template-free solvothermal method. X-Ray diffraction patterns demonstrated that the products are pure monoclinic WO₃. Based on the observation of scanning electronic microscopy (SEM) and transmission electron microscopy (TEM), it was revealed that the as-prepared WO₃ nanospheres have a diameter of around 2 μm and are hollow structures with shell thickness of about 300 nm which are constructed by numerous oriented nanocrystals. Sensors based on the synthesized WO₃ hollow nanospheres exhibited high selectivity to NO₂ at low operating temperature. The detection limit can be as low as ∼40 ppb level.