Mn₂O₃ has been demonstrated to be a promising electrode material for lithium-ion batteries. Thus, the fabrication of Mn₂O₃ nanomaterials with high specific capacity and cycling stability is greatly desired. Here we report a simple but effective method to synthesis Mn₂O₃ nanomaterials from a Mn(OH)₂ precursor, which was prepared from manganese acetate in ethylene glycol and water at 180 °C for 12 h. The morphology and sheet thickness of Mn(OH)₂ precursor could be tuned by controlling the ethylene glycol/H₂O volume ratio, resulting in a further tunable morphology and sheet thickness of the porous Mn₂O₃ nanomaterials. In the electrochemical tests the prepared Mn₂O₃ nanomaterials, with the porous architecture and thin thickness exhibited a high and stable reversible capacity, indicating that both small thickness and porous sheets structure are crucial for improving the electrochemical performance of Mn₂O₃ in terms of specific capacity and stability.