Size-controlled synthesis of nickel nanocrystals by the decomposition of nickel acetylacetone in a noncoordinating reagent, oleylamine, was studied. Three processes were employed to synthesize nanocrystals with diameters in the range of 20-60 nm. The resultant nanoparticles were characterized to be single-phase nanocrystalline nickel with a face-centered cubic type. Mechanism of the size-controlled nanocrystals formation was studied and found that relative monodispersed nanocrystals could be formed by the separation of nucleation and growth process while the size could be controlled through modulating growth period. Magnetic measurements showed that samples were still ferromagnetic, and that their saturation magnetization and coercivity are size-dependent. (c) 2005 Elsevier Ltd. All rights reserved.