Monodisperse and uniform pure and Cu-doped alpha-Fe₂O₃cubes with a hierarchical architecture piled up nanoparticles as secondary units were obtained via a low-cost and environmentally friendly hydrothermal route. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction (XRD)，field-emission electron microscopy (FESEM)，and transmission electron microscopy (TEM). The XRD results indicated that the lattice constants of doped samples were slightly smaller than that of the pure sample due to Cu incorporation. A comparative gas sensing study between the Cu-doped alpha-Fe₂O₃and pure alpha-Fe₂O₃cubes was performed to demonstrate the superior gas sensing properties of the doped samples. It was found that the sensor based on Cu-doped alpha-Fe₂O₃(3.0 wt%) had a response of 19-100 ppm C₂H₅OH，which was about three times higher than that of the pure alpha-Fe₂O₃nanostructures at the same operating temperature (225℃).