Nickel nanoparticles were synthesized by the chemical reduction of NiCl 2 with N 2 H 4 under controlled pH environment. During nucleation, polyvinyl pyrrolidone (PVP) was added as the protective agents for preventing the agglomeration of metal clusters. Color of the solution changed from green to blue during the reaction period. X-Ray Adsorption Spectroscopy (XAS), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (TEM) analytical methods were used to characterize the product. XAS analysis showed that the reduction reaction occurred within 5 minutes after the addition of N 2 H 4. The length of Ni-Ni bond was 2.59 nm. The results of XRD analysis of the three cases with pH ranging from 11.0 to 13.0 suggest that the optimum pH value for the reaction appeared to be 12.0. The average particle size was 20–50 nm under this condition.