Cubic boron nitride (c-BN) crystals with a dimension of 0.3-0.4 mm, which have been synthesized using lithium nitride (Li3N) as a catalyst under high temperature-high pressure (HPHT), were examined by transmission electron microscopy (TEM). It was shown by TEM that there exits some nanostructrued areas containing several types of nanosized foreign particles within the as-grown c-BN crystals. The results indicate that the nanometer inclusions are hexagonal BN (h-BN) with a lattice constant of a=2.054 Angstrom, c=6.661 Angstrom, tetragonal B25N with a lattice constant of a=8.79 Angstrom, c=5.08 Angstrom, tetragonal B53N with a lattice constant of a=8.79 Angstrom, e=5.08 Angstrom, and hexagonal Li3N with a lattice constant of a=3.648 Angstrom, c=3.875 Angstrom. (C) 2002 Elsevier Science B.V. All rights reserved.