Fe3C carbide was treated at a high temperature of 1630 K and a high pressure of 5.3 GPa (HPHT) in a cubic anvil apparatus. Diamond is found to form from iron carbide at high temperature-high pressure (HPHT). The formation of the diamond can be confirmed by laser Raman spectra. This work opens a new way to synthesize diamond at HPHT and provides direct evidence about the diamond formation mechanism in the presence of a transition metal catalyst using graphite as the carbon source at HPHT. (C) 2002 Elsevier Science B.V. All rights reserved.