We report a mild template-free hydrothermal route for selective synthesis of SnO2 hollow microspheres and nano-sheets using SnCl2 and NaOH as initial materials.By switching the solvent from water to ethanol,the formed SnO2 nanostructures changed from nano-sheets to hollow microspheres.The obtained nano-sheets were single crystalline in structure.On the basis of the characterization of intermediate products,the formation of SnO2 hollow microspheres was ascribed to a crystal growth process,while the formation of SnO2 nano-sheets was ascribed to the oxidation of SnO2 sheets during the hydrothermal process.Further characterization of the SnO2 hollow microspheres and nano-sheets by X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy reveals different optical absorption properties and valence band electronic structures.In addition,the SnO2 nano-sheets and hollow microspheres exhibit different sensing properties.The present work provides a facile and simple template-free method for the synthesis of nano-structured SnO2. We report a mild template-free hydrothermal route for selective synthesis of SnO2 hollow microspheres and nano-sheets using SnCl2 and NaOH as initial materials. By switching the solvent from water to ethanol, the formed SnO2 nanostructures changed from nano-sheets to hollow microspheres. The resulting nano-sheets were single crystalline in structure. On the basis of the characterization of intermediate products, the formation of SnO2 hollow microspheres was ascribed to a crystal growth process, while the formation of SnO2 nano-sheets was ascribed to the oxidation of SnO2 sheets during the hydrothermal process. Further characterization of the SnO2 hollow microspheres and nano-sheets by X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy reveals different optical absorption properties and valence band electronic structures. In addition, the SnO2 nano-sheets and hollow microspheres exhibit different sensing properties. The present work provides a facile and simple template-free metho d for the synthesis of nano-structured SnO2.