When a topological defect such as 5- or 7-membered ring is introduced in a hexagonal lattice of graphene, it makes curved nature. It is essential to understand how the topological defects in a carbon nanotube (CNT) is introduced, migrated and eliminated, since it may enable us to design many types of CNT-based hybrid structures showing unique properties. In this paper, some experimental studies on deformation process of individual CNTs by transmission electron microscopy is introduced.