Monocrystalline orthorhombic Na0.44MnO2 nanoplate as a potential cathode material for sodium-ion batteries has been synthesized by a template-assisted sol-gel method. It exhibits high crystallinity, pure phase and homogeneous size distribution. During the synthesis, acidic and reductive conditions are applied to limit the production of unfavorable Birnessite phase in the precursor, and colloidal polystyrene is included to avoid morphology collapse during the gel formation and particle elongation in one direction. The decompositions of polystyrene and citric acid during high temperature firing offer a reductive carbothermal condition which can suppress the formation of unidimensional particles, and limit particle growth along the [001] direction. As a consequence, the material delivers 96mAhg−1 discharge capacity at 10C (86% of 0.1C capacity) and maintains 97.8% capacity after 100 cycles at 0.5C. Such superior rate capability and cycling stability of this material are among the best to date, suggesting its great interest in practical applications.