Phase-pure Cu 4O 3 microspheres were synthesized for the first time via a facile solvothermal method, using Cu(NO 3) 2·3H 2O as the precursor. A formation mechanism was proposed based on the observation of a series of reaction intermediates. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction and oxidation, X-ray photoelectron spectroscopy, and nitrogen adsorption. It was found that the composition of the prepared products were highly dependent on the synthesis conditions, particularly the hydrate water content in the copper precursor of Cu(NO 3) 2. Pure Cu 4O 3 microspheres with a diameter of 2-10 μm could be obtained via the symproportionation reaction (2CuO + Cu 2O → Cu 4O 3), which was regarded not being feasible in aqueous media under mild synthesis conditions. The electrochemical properties of the Cu 4O 3 microspheres as anode materials for Li-ion batteries were also investigated. Compared to the simple physical mixture of CuO and Cu 2O with an equivalent atomic ratio of 2:1, the as-prepared Cu 4O 3 exhibited unique lithium storage behaviors at a low voltage range and superior electrochemical performances as an anode material for Li-ion batteries. The successful preparation of pure Cu 4O 3 material could provide opportunities to further explore its physicochemical properties and potential applications.