Urchin-like InOOH microspheres were successfully prepared by a convenient and controllable method. Such experimental parameters as solvents and complexing reagents on the formation of the urchin-like InOOH microspheres were investigated. Scanning electron microscopy, X-ray diffraction and infrared spectroscopy were employed to investigate the evolution process of the urchin-like InOOH precursors. Furthermore, the formation mechanism of the urchin-like InOOH microspheres was proposed. By annealing the urchin-like InOOH precursor at different temperatures under ambient pressure, rhombohedral corundum-type indium oxide (rh-In2O3), cubic bixbyite-type indium oxide (c-In2O3) and mixed phases of rh-In2O3 and c-In2O3 were obtained. The gas sensing properties of the prepared In2O3 samples were examined. It was found that the sensors based on the prepared In2O3 samples exhibited excellent response and selectivity to formaldehyde. (C) 2014 Elsevier Ltd. All rights reserved.