Dense spherical Ni particles were prepared from nitrate solution by spray pyrolysis in a H2–N2 atmosphere. Hollow NiO particles with rough surfaces were formed first at low temperature and then reduced to Ni by H2 above 300°C. Subsequent intraparticle sintering of the Ni crystallites gave rise to densification of Ni particles as the temperature was raised; most Ni particles became dense above the pyrolysis temperature of 1000°C. However, when a N2 atmosphere was used, hollow NiO particles were formed, which did not densify even at 1200°C due to the lack of sintering. The dense Ni particles obtained were of good crystallinity and good oxidation resistance, especially for those formed at higher pyrolysis temperatures and longer residence times.