α-Fe2O3 polyhedrons have been successfully synthesized via a one-pot hydrothermal process. The average diameter of the synthesized α-Fe2O3 polyhedrons is about 0.8 μm. The structure and morphology of α-Fe2O3 polyhedrons were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. And the possible formation mechanism is proposed that the α-Fe2O3 polyhedrons are grown epitaxially from the FeOOH precursors by topotactic transformation. The experimental parameters play a crucial role in the growth of the α-Fe2O3 polyhedrons. The results indicate that the phase and morphology of the products are greatly affected by the concentrations of disodium ethyleediamine tetracetate and NaOH in the starting solution. The magnetic properties of α-Fe2O3 polyhedrons show weak ferromagnetic behavior with the saturation magnetization of 0.498 emu/g, remanent magnetization of 0.051 emu/g and coercivity of 372.81 Oe.