Nickel oxide nano-particles were prepared successfully by thermal decomposition of the β-Ni(OH)2 in this work. The precursor β-Ni(OH)2 was obtained by the chemical precipitation reaction of Ni(NO3)2 and KOH at near room temperature. The grain growth kinetic of nano-sized nickel oxide for thermal treatment process was studied by means of isothermal and isochronal annealing. The results showed the precursor β-Ni(OH)2 is spindle alike shape, which can transform entirely into cubic NiO nano-particles when calcinated at temperature higher than 280°C. The NiO nano-particles grew up with the increasing of the calcinating temperature and the prolonging of the calcinatiing time. Moreover, we found that to tune the annealing temperature is more available for size controlling than to vary the annealing time. The grain growth kinetic of NiO nano-particles is found to follow the equation D7 = 1.946×1017•t•exp(-1.466×103/RT), where the grain growth exponent and an activation energy are n=7 and Ea=146.56KJ/mol, respectively.