Under refluxing conditions in alcoholic solution, nickel sea-urchin-like particles and nickel spherical nanoparticles self-assembled into nanochains have been synthesized by a simple wet chemical method in which aqueous hydrazine (N2H4 center dot H2O) was used as reducing reagent and sodium hydroxide (NaOH) was used as alkaline reagent. The structure and morphology of the final nanoparticle products are controlled by the adding sequence of N2H4 center dot H2O, NiCl2, and NaOH solutions. The sea-urchin-like Ni particles and the spherical Ni nanoparticles self-assembled into nanochains were obtained by varying the adding sequence of these reactants. In addition, a relatively higher temperature is advantageous to the formation of both sea-urchin-like and chain-like Ni nanoparticles. Finally, the dependence of the magnetic parameters such as coercivity (H-c) and squareness (M-gamma/M-s) on the morphology of as-prepared Ni nanocrystals will be discussed. (c) 2008 Elsevier B.V. All rights reserved.