A liquid/liquid interfacial reaction system was designed to fabricate α-Fe2O3 cubes. The reaction system uses a hydrophobic ionic liquid containing iron ions ([(C8H17)2(CH3)2N]FeCl4) for manufacturing α-Fe2O3 cubes by a novel and environmentally friendly hydrothermal method under low-temperature conditions (140 °C). The iron-containing ionic liquid is hydrophobic and can form a liquid/liquid interface with water, which is vital for fabrication of the α-Fe2O3 cubes. Nanomaterials synthesized from hydrophobic iron-containing ionic liquids show good crystallinity, well-developed morphology, and uniform size. The effect of different ionic liquids on the morphology of α-Fe2O3 was investigated in detail. [(C8H17)2(CH3)2N]FeCl4 is assumed to perform the triple role of forming a liquid/liquid interface with water and acting as reactant and template at the same time. The effect of the reaction temperature on the formation of the α-Fe2O3 cubes was also studied. Temperatures lower or higher than 140 °C are not conducive to formation of the α-Fe2O3 cubes. Their photoelectrochemical properties were tested by means of the transient photocurrent response of electrodes modified with as-prepared α-Fe2O3 cubes. The photocurrent response of an α-Fe2O3 cubes/indium tin oxide electrode is high and stable, and it shows great promise as a photoelectrochemical glucose sensor with high sensitivity and fast response, which are beneficial to practical applications of nanosensors.