Several straight hetero-junctions carbon nanotubes (CNTs) are constructed and their tensile behavior are investigated. It is pointed that the Young's modulus of hetero-junctions is lower than the values of their fundamental homogeneous CNTs due to the existence of pentagon–heptagon pair defects. In addition, it is revealed that the Young's modulus of homogeneous zigzag CNTs increases by increasing the chiral number of these nano-structures. Finally, it is concluded that as the connecting length of the hetero-junctions increases the Young's modulus of these particular CNTs decreases. Therefore, the tensile strength of hetero-junctions depends on the presence of pentagon–heptagon pair defects.