The α-Fe2O3 hierarchical nanostructures have been successfully synthesized via a simple solvothermal method. The as-prepared samples are loose and porous with flowerlike structure, and the subunits are irregularly shaped nanosheets. The morphology of the α-Fe2O3 structures was observed to be tunable as a function of reaction time. To demonstrate the potential applications, we have fabricated a gas sensor from the as-synthesized hierarchical α-Fe2O3 and investigated it for ethanol detection. Results show that the hierarchical α-Fe2O3 sensor exhibits significantly improved sensor performances in comparison with the compact α-Fe2O3 structures. The enhancement of sensing properties is attributed to the unique porous and well-aligned nanostructure.