This paper reports a hydrothermal conversion of MnOOH needles into orthorhombic LiMnO2 nanorods for lithium ion battery application. XRD investigation indicated phase conversion during the Li ion incorporation, and several intermediate phases were formed during the hydrothermal reaction. SEM observation of the sample powder revealed morphological changes during the process, showing that LiOH, not only worked as the Li ion source during the incorporation, but also served as the corrosive media to create nanorod like shape. TEM observation revealed the single crystalline nature of the nanorods and a preferred growth direction along b axis direction was also determined. o-LiMnO2 nanorods prepared by such hydrothermal routine showed high electric capacity and stable cyclability at current density of 1/10C, indicating potential application in the lithium ion battery field.