A hierarchical NiO-based nanostructure, constructed from multi-dimensional building blocks, was fabricated by a synthesis method based on electrospinning and solution phase reaction. Fe was incorporated into the NiO nanostructure with highly uniform distribution via ion exchange reaction. A series of Fe2O3/NiO composites with different compositions were successfully synthesized with the hierarchical architecture well preserved. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) were used to characterize the structure and to confirm the formation mechanism of the synthesized products. The gas sensing properties of the Fe2O3/NiO hierarchical composites were systematically investigated. The optimized composition of Fe2O3/NiO shows superior sensing performance towards ethanol, such as high sensitivity, fast response/recovery speed and good selectivity. The high gas sensing performance of the sensing material was mainly due to the completeness of the heterojunction assembly between n-type Fe2O3 and p-type NiO, as well as the amplification effect caused by assembling the heterojunctions on the nanoscale.