Single crystals of cubic boron nitride (cBN) were synthesized from amorphous boron nitride (aBN) under static high pressures and temperatures (40-50 kb, 1200-1500degreesC) using Mg-Al alloy catalyst-solvent material. The weight percentage of magnesium in the alloy powder was about 40%. It was found that aBN containing small amount of B2O3 as an oxide impurity transforms easily into cBN (in the thermodynamically stable region of cBN) whereas aBN powder without B2O3 did not transform into cBN to the same extent under the similar P-T conditions. It appears therefore, that the presence of oxide impurity in aBN powder facilitates the transformation of aBN into cBN although it does not have any catalytic action for aBN-cBN phase transformation. (C) 2003 Elsevier B.V. All rights reserved.