Nanocrystalline nickel monosulfide was prepared with NiCl2. 6H(2)O and Na2S3 as the reactants and Zn as the reductant, via a solve-thermal reducing process at 80-120 degrees C. X-ray diffraction analysis indicated that the product was the hexagonal phase of NiS. Transmission electron microscopy showed that the average particle size was about 30 nm. The reaction route of the formation of NiS is also discussed. (C) 2000 Elsevier Science Ltd.