Pure and Cu-doped hierarchical flower-like In₂O₃microspheres constructed from numerous nanosheets have been successfully synthesized via a facile and efficient solvothermal route combined with the subsequent thermal treatment. Various techniques, including X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) were employed to acquire the crystalline and morphological information of the as-obtained samples. XRD measurement results apparently revealed that the lattice constants of doped products were slightly smaller than that of the pure products owing to Cu incorporation. Gas sensing performances of the sensor devices fabricated from undoped and Cu-doped In₂O₃were systematically investigated. It was demonstrated that the Cu-doping significantly improved the response to NO₂. For example, sensors based on Cu-doped In₂O₃(1.0 mol%) give a response of about 1800-400 ppb NO₂, which was about 14.5 times higher than sensors based on primary In₂O₃microstructures. The excellent and enhanced NO₂sensing performances of Cu-doped In₂O₃were associated to its novel hierarchical structure and the incorporation of Cu ions.