Single-crystalline potassium tungsten bronze nanosheets were prepared by reducing potassium tungsten oxide nanosheets grown on a W foil. The nanosheets showed no evident shape change before and after reduction. Morphology, structure, and composition analyses revealed that a phase transformation from orthorhombic potassium tungsten oxide to hexagonal potassium tungsten bronze occurred. Better field emission with lower turn-on field was measured from potassium tungsten bronze nanosheet film. The effects of reduction treatment on field emission performance are discussed.