NiO nano-crystal powders with cubic structure were synthesized by molten salt method. The synthesized materials were characterized by XRD, TEM, N2 adsorption-desorption and TG, etc. Not only are the eminent characters of weak agglomeration, narrow distribution and fine crystalline configuration, but the average crystal sizes of synthesized NiO powders could be efficiently controlled from 10 nm to 100 nm by changing the calcination conditions, such as calcination temperature, calcination time, and proportion of molten salt KNO3. Molten salt method is technologically easy and cheap, for the production of NiO nano-crystal powders in industrial scale.