Herein, ultra-small gold nanoparticles are decorated onto NiO nanobelts using HAuCl4 and Ni(OH)2 nanobelts as precursors via a one-step thermal treatment, and a temperature of 500 °C is used for the decomposition of both precursors at the same time; the amount of gold nanoparticles in the electrode materials ranges from 0 to 17.38 wt%; moreover, the effect of the gold content on the structure and electrochemical performance has been investigated. The results show that the fabricated materials achieve a high specific capacitance of 597 F g-1 with a Au content of 1.54 wt%, and the Au grain size is about 12.0 nm. An asymmetric supercapacitor device was assembled using gold nanoparticle/NiO as the positive electrode and activated carbon as the negative electrode, which exhibited a maximum energy density of 18.0 W h kg-1 and an excellent cycle life, retaining 84% of the initial specific capacitance after 22 000 cycles.