Synchrotron small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), and transmission electron microscopy were carried out for an oriented polyethylene-block-[atactic poly(propylene)] with a molecular weight of 1.13 x 10(5) and a volume fraction of polyethylene of 0.5. Isothermal crystallization at 93 degreesC did not destroy the pre-formed microdomain, however, with a higher crystallization temperature, the microdomain was more heavily deformed and more crystalline lamella grew. In WAXS profiles, preferential orientation of (020) reflection peak was observed, indicating that the crystalline lamella grew in parallel with the micro domain interface.