Nanocrystalline nickel powders were prepared in aqueous solution through a thermal-reduction process. The reductive atmosphere was produced from the disproportionation of white phosphorus in basic solution at 100 degrees C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis were employed to characterize the products. XRD revealed that the nickel was single phase. TEM showed that the average particle size was about 26 nm. The purity of the as-prepared nickel was 99.6%, as determined from the spectrophotoscopy. The possible formation mechanism of nanocrystalline nickel is a reduction of nanocrystalline Ni(OH)(2).