Cellular interface in diamond grown from Fe-Ni-C system under high-pressure has been elucidated. The diamond growth stability is broken and planar growth front interface transforms into cellular interface due to the existence of a narrow constitutional supercooling zone in front of diamond-solution boundary layer. Under growth parameters fluctuating, the solution in channels of cellular interface with high-solute concentration is trapped in diamond and crawls along direction of temperature gradient. In the presence of cellular interface, the grown diamond is always inhomogeneous in inclusion distribution and imperfect with structural defects. The lineally distributed inclusions closely associated with the cellular interface were clearly observed. (C) 2002 Published by Elsevier Science B.V.