The fabrication of single crystalline Li0.44MnO2 nanowires for the positive electrode of lithium ion battery is reported. The single crystalline Li0.44MnO2 nanowires are obtained by lithium exchange reaction of Na0.44MnO2 nanowires with high aspect ratio. The Li0.44MnO2 nanowires indicate both the large specific capacity of around 250mAhg−1 (1.5–4.5V vs. Li/Li+) and the good high current density property for the positive electrode of lithium ion battery.