The Ni formation behavior from the reduction of NiO nano crystals in the $H_2/N_2$ gas mixtures. The NiO nano crystals were synthesized by heat-treating nickel nitrate$(Ni(NO_3)_2cdot6H_O)$ in the air at $500^{circ}C$, and had an octahedral shape and the particle size of 200~500 nm. The NiO nano-crystals had well-developed (111) planes which is hardly formed in normal synthetic conditions. The reduction process was carried out at 300 and $600^{circ}C$ for 15 and 60 minutes, respectively. When the NiO nano-crystals were reduced at $300^{circ}C$, the Ni particles sustained the same octahedral shape as NiO, while Ni particles were to agglomerate at $600^{circ}C$.