Orthorhombic LiMnO2 nanoparticles and LiMnO2 nanorods have been synthesized by hydrothermal methods. LiMnO2 nanoparticles were synthesized by simple one-step hydrothermal method. To obtain rod-like LiMnO2, γ-MnOOH nanorods were first synthesized and then the H+ ions were completely replaced by Li+ resulting in LiMnO2 nanorods. Their electrochemical performances were thoroughly investigated by galvanostatic tests. Although the LiMnO2 nanoparticles have smaller size than LiMnO2 nanorods, the latter exhibited higher discharge capacity and better cyclability. For example, the discharge capacities of LiMnO2 nanorods reached 200 mA·h/g over many cycles and remained above 180 mA·h/g after 30 cycles. However, the maximum capacity of LiMnO2 nanoparticles was only 170 mA·h/g and quickly decreased to 110 mA·h/g after 30 cycles. Nanorods with one-dimensional electronic pathways favor the transport of electrons along the length direction and accommodate volume changes resulting from charge/discharge processes. Thus the morphology of LiMnO2 may play an important role in electrochemical performance.