A facile and surfactant-free approach for the synthesis of well-defined mesoporous nanocrystalline SnO2 has been presented. This method involves hydrothermal treatment of tin chloride with urea in a mixed solvent of ethanol and water in the presence of ammonium sulfate. The as-prepared material has a high crystallinity and a well-defined mesoporous structure. The pore size evolution and surface properties of the synthesized nanocrystalline mesoporous SnO2 powders are characterized in detail by X-ray diffraction, N-2 adsorption/desorption isotherms, transmission electron microscopy, thermal analysis, and Fourier transform infrared techniques.