Abstract: Disclosed is a method for preparing hematite iron oxide having various nanostructures, including: preparing a mixture solution by adding iron chloride and caffeine to a solvent and magnetically stirring; and performing hydrothermal synthesis, wherein the solvent is selected from water, ethanol, propanol and methanol. In accordance with the present disclosure, hematite iron oxide (?-Fe2O3) superstructures of various shapes, including grape, cube, dumbbell and microsphere shapes, can be synthesized in different solvents using caffeine. The shapes can be controlled variously via a simple one-step synthesis route without using a growth-inducing agent and without separation based on size. The prepared hematite iron oxide exhibits high coercivity at room temperature owing to its fine crystal structures and anisotropic shapes.