Tungsten oxide has attracted considerable attention as a typical photochromic material. Herein, a simple route for the synthesis of tungsten oxide quantum dots (WO3-x QDs) was demonstrated which was accomplished by the hydrothermal treatment of ammonium tungstate hydrate in the present of polyvinyl pyrrolidone (PVP). This photochromic material can rapidly undergo a color change reaction under the irradiation of ultraviolet or solar light. More importantly, the bleaching can be completed in a dark environment for 5 min and the cycle stability is excellent. The ultra-small size, existence of oxygen deficiency, and the surface modification by PVP are attribute to fast photochromic performance, excellent reversibility and cycling stability of WO3-x QDs.