The morphology formed in binary blends of poly(epsilon-caprolactone) (PCL) and epsilon-caprolactone-butadiene diblock copolymer (PCL-b-PB) has been investigated by small-angle X-ray scattering (SAXS). The difference in the microdomain structure in the melt yielded different morphologies after crystallization : when PCL dispersed uniformly in the PCL domain in the melt, the morphology was an alternating structure composed of lamellae and amorphous layers (lamellar morphology). When PCL was localized within the PCL domain, a mosaic structure of two lamellar morphologies, each consisting of a PCL region and a PCL-b-PB-rich region, was formed over a limited composition range.