Mixed-phase iron oxide nanocomposites (abbreviated as m-Fe2O3) of hematite (α-Fe2O3) and magnetite (γ-Fe2O3), using potassium ferricyanide (K3[Fe(CN)6]) as the precursor, are successfully synthesized via a simple two-step approach incorporating a hydrothermal reaction and the subsequent thermal annealing. The crystalline structures, specific surface areas and surface morphologies of the as-prepared m-Fe2O3 are characterized in detail by X-ray diffraction (XRD), nitrogen sorption analysis and scanning electron microscopy (SEM), respectively. The electrochemical performances of m-Fe2O3 are examined by galvanostatic cycling and cyclic voltammetry (CV). Transmission electron microscope (TEM), High resolution TEM (HRTEM), selected area electron diffraction (SAED) and Raman are used to investigate the nanocrystalline and composition of the materials. Compared to α-Fe2O3, m-Fe2O3 exhibits a much more excellent cycling stability with a typical discharge specific capacity of 982 mAh g−1 after 50 cycles at a current density of 100 mA g−1, which is attributed to α-Fe2O3 converted to γ-Fe2O3 during charge–discharge cycling. The superior performance of m-Fe2O3 to α-Fe2O3 would provide a new perspective about the effect of mixed-phase on improving the electrochemical properties of lithium-ion batteries.