The synthesis of nickel nanoparticles by the hydrazine reduction of nickel chloride in ethylene glycol at 60 degreesC without soluble polymer as a protective agent was studied. It was found that an appropriate amount of NaOH was necessary for the formation of pure nickel nanoparticles. Also, it was not necessary to perform the reaction under a nitrogen atmosphere. By the analyses of X-ray diffraction, high-resolution transmission electron microscopy, and electron diffraction pattern, the resultant particles were characterized to be pure crystalline nickel with a face-centered cubic (fcc) structure. By transmission electron microscopy, it was observed that the mean diameter decreased with increasing the ratio of [N2H5OH]/[NiCl2] and approached a constant when [N2H5OH]/[NiCl2] > 12. In addition, the resultant nickel nanoparticles could be magnetically recovered and re-dispersed in ethylene glycol without size change and agglomeration. The magnetic measurements indicated they were superparamagnetic with a saturation magnetization of 22 emu/g, a remanent magnetization of 6.4 emu/g, and a coercivity of 0.1 Oe at a mean diameter of 9.2 nm. Also, the magnetization increased with decreasing temperature due to the decrease in thermal energy. All the observed magnetic properties essentially reflected the nanoparticle nature. Furthermore, it was found that hydrazine was catalytically decomposed to hydrogen and nitrogen gases by the resultant nickel nanoparticles. The corresponding decomposition rate at 25 degreesC and 1 atm was 3.1 nmol/(h mg of Ni). (C) 2003 Elsevier Science (USA). All rights reserved.