Nanocrystalline perovskite KNbO3 is prepared by a peroxo-precursor decomposition method at moderate temperatures of 650-900 degrees C. Peroxo-heteropoly-niobic acid is prepared by direct reaction between NbC powder and H2O2 aq, and mixing the peroxo-heteropoly-niobic acid with KOH aq yields an amorphous precursor salt. Perovskite KNbO3 is obtained by heating the precursor in air for 1 h at 650-900 degrees C. The X-ray diffraction patterns were well fitted with the space group Pm3m in the Rietveld analysis. The X-ray diffraction peak profiles and field emission scanning electron microscope images indicate the crystallite size is in the range of 25-35 nm. (C) 2010 Elsevier Ltd. All rights reserved.