The fracture behavior of the diamond single crystals with metallic inclusions was investigated in the present paper. Single diamond crystals with metallic inclusions were formed by a special process with high pressure and high temperature (HPHT). The inclusions trapped in the diamond were characterized mainly to be metallic carbide of (Fe,Ni) 23 C 6 or Fe 3 C and solid solution of γ-(Fe,Ni) by transmission electronic microscopy (TEM). The grain size of the inclusions is about micrometers. The fracture characteristics of the diamond single crystals, after compression and heating, were investigated by optical microscopy (OM) and scanning electron microscopy (SEM). The fracture sections of the compressed and heated diamonds were found to be parallel to the (111) plane. The interface of the inclusions and diamond is deduced to be the key factor and the original region of the fracture formation. Mechanisms of the fracture behavior of the HPHT synthesized diamonds are discussed.