Although human eyes are quite insensitive to ultraviolet (UV) light, most of the longer wavelength UV light (the UV-A band between 320 and 400 nm) does reach the earth surface and after prolonged exposure, the radiation can cause health concerns especially skin cancer. Therefore, it is extremely important to explore ways to effectively monitor the radiation. Herein we report for the first time a new high-performance UV photodetector made of an individual Nb2O5 nanobelt. Quasi-aligned Nb2O5 nanobelts 100–500 nm wide and 2–10 μm long were synthesized using a hydrothermal treatment of a niobium foil in a KOH solution followed by proton exchange and calcination treatment. A nanostructured photodetector was constructed from an individual Nb2O5 nanobelt and its optoelectronic properties were evaluated. The detector exhibited linear photocurrent characteristics, excellent light selectivity, and high external quantum-efficiency (EQE) of 6070%. Long-term stability of the photocurrent over a period of 2500 s at an applied voltage of 1.0 V was achieved. The photodetector performance was further enhanced by improving the crystallinity and eliminating the defects in the Nb2O5 nanobelt crystals. These excellent optoelectronic properties demonstrate that Nb2O5 nanobelts are suitable for visible-blind UV-light sensors and optoelectronic circuits, especially those operating in the UV-A range.