Mesoporous uniform ammonium nickel phosphate hydrate nanostructures are successfully prepared by a one-pot hydrothermal method. As a result of the unique feature of large surface area (418 m² g⁻¹) and tunable mesostructures, the material exhibits good performance as supercapacitor electrodes, with a specific capacitance of 1072 F g⁻¹ in 3.0 M KOH at a current density of 1.50 A g⁻¹, and show a good cycle life which does not obviously decay after 3000 cycles (the retention 95.0% of initial specific capacitance after 3000 cycles).