The emergence of one-dimensional (1D) micelles obtained from the crystallization driven self-assembly (CDSA) in solution of crystalline-coil block copolymers has opened the door to the fabrication of a variety of sophisticated structures. While the development of these fascinating nanomaterials is blossoming, there is very little fundamental work dedicated to understanding the morphological evolution of these 1D micelles in solution. Here, using a combination of transmission electron microscopy, electron tomography, and static and dynamic light scattering, we studied the effect of annealing on a colloidal suspension of 1D micelle fragments formed by the self-assembly of a crystalline-coil poly(ferrocenyldimethylsilane)-block-poly(isoprene) (PFS-b-PI) block copolymer in decane, a solvent selective for PI. We are particularly interested in studying the evolution of the rectangular cross-section of the crystalline core of these micelle fragments. By electron tomography, we observed that the shorter dimension of the cross-section became even thinner upon annealing at elevated temperatures, while the longer dimension increased. In parallel, we observed an increase in packing density of the crystalline block as the fragments were annealed at temperatures above 60 °C. From these results, we concluded that annealing the micelle fragments induces a thinning of the crystalline core coupled with a lateral growth.