There has been a considerable amount of research on MFCNTs and MFCNFs; however, research on the behavior of the internal metal used in MFCNF under heating has been limited. Therefore, in this study, an MFCNF was heated and the behavior of the internal metal was investigated using in-situ TEM observations. The internal metal used in the MFCNF did not melt. It was supposed that the non-melting was because of the high pressure of the internal metal resulting from a difference in the coefficients of linear thermal expansion of the graphite wall of the MFCNF and the internal metal. The pressure of the internal metal was calculated; it was approximately 12 GPa when the MFCNF was heated at 1500 degrees C. (C) 2010 Elsevier B.V. All rights reserved.