The morphology, formed by the crystallization of epsilon-caprolactone blocks in a crosslinked microdomain structure of poly(epsilon-caprolactone)-block-polybutadiene (PCL-b-PB), has been investigated by wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (d.s.c.). The WAXD results showed that even in the crosslinked PCL-b-PB, PCL blocks crystallized in the same crystal form as PCL homopolymers. The SAXS measurements revealed that the microdomain structure in the melt remained unchanged by the subsequent crystallization, indicating that the PCL blocks crystallized within this structure. This point is extremely different from the case of the uncrosslinked PCL-b-PB, where a dramatic morphological reorganization takes place by the crystallization; a microdomain structure is completely replaced by an alternating structure of lamellae and amorphous layers. The melting temperature and crystallinity of the PCL blocks in the crosslinked PCL-b-PB were significantly reduced compared with those of the uncrosslinked PCL-b-PB, suggesting that the fixed microdomain structure affected significantly the crystallization of the PCL blocks to yield imperfect crystals within this structure.