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 (N 2 H 4 ·H 2 O) 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 N 2 H 4 ·H 2 O, NiCl 2 , 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 γ /M s ) on the morphology of as-prepared Ni nanocrystals will be discussed.