We report a nanostructured oxide pseudocapacitor electrode utilizing a sodium-doped vanadium oxide (β-Na_0.33V₂O₅) nanobelt network with a three dimensional framework crystal structure, which has been successfully synthesized under mild hydrothermal conditions and heat treatment. Cyclic voltammetry, galvanostatic charge-discharge and cycling tests have been carried out on the nanobelt network in 1 M LiClO₄/propylene carbonate (PC) electrolyte for a 1 V potential window. A high specific capacitance of 320 F g⁻¹ at 5 mV s⁻¹ scan rate has been achieved with two sets of redox peaks being identified, corresponding to the half occupancy at M₃ and M₂ intercalation sites along the tunnel in the β-Na_0.33V₂O₅ crystal lattice. The β-Na_0.33V₂O₅ nanobelt electrode is able to deliver a high energy density of 47 W h kg⁻¹ at a high power density of 5 kW kg⁻¹. Slight degradation in energy density at high power density has been observed. This can be attributed to the charge storage in the nanobelt network which is dominated by the fast surface dependent reaction. Superior cycling stability, with only 34% degradation in specific capacitance, is observed in the β-Na_0.33V₂O₅ nanobelts after 4000 cycles. The results clearly indicate the promising potential of these doped vanadium oxide electrodes for electrochemical energy storage devices.