Nickel particles were prepared by spray pyrolysis of 0.5 M Ni(NO3)(2).6H(2)O solution with hydrogen at a residence time of 19 s. All the product particles were composed of nickel oxide and nickel with no trace of nickel nitrate under the condition. The particles were completely reduced to nickel at a furnace set temperature of 410 degreesC. However, it was not until 850 degreesC that the spherical particles fully densified and crystallized appeared. Use of urea enhanced the solidness and surface smoothness of the particles, while slightly reducing the rate of metallization. The urea enabled to prepare the nickel particles even without hydrogen though under stricter conditions. The rates of metallization and sintering/crystallization were slightly affected by the residence time and initial salt concentration. Higher crystallized nickel particles had higher resistance to oxidation in air environment. (C) 2004 Elsevier B.V. All rights reserved.