The present study aims to deduce the in-situ response of iron carbide (Fe3C) nanorod filled inside carbon nanotube ( CNT) under electron irradiation. Electron irradiation on Fe3C filled-CNT at both high and room temperature (RT) has been performed inside transmission electron microscope. At high temperature (HT), it has been found that gamma-Fe atoms in lattice of Fe3C nanorod accumulate first and then form the cluster. These clusters follow the inverse Ostwald ripening whereas if e-irradiation is performed at RT then only the morphological changes in both carbon nanotube as well as nanorod are observed. Compression generated either by electron beam heating or by shrinkage of CNT walls is observed to be a decisive factor. (C) 2015 Elsevier B.V. All rights reserved.