Nanocrystalline nickel powders were prepared by irradiating the aqueous solution of NiSO,4, with γ-ray, using AgNO,3, as nucleation agent. It was found that the pH value of the system before irradiation affected the composition of products and alkalinity of solution was necessary to prepare nickel nanopowders. The characterization of products with transmission electron microscope (TEM) and X-ray photoelectron spectrum (XPS) indicated that the powders were fibrelike nickel particles (diameter ,<,10nm) . Metallic silver, as crystal nucleus,was wrapped up in metallic nickel. The existence of AgNO,3, not only supplied the aggregation center, but also affected the micromorphology of products.