Narrow banded structures of spherulites of poly [(R)-3-hydroxybutyrate] (P(3HB)) and its copolymers, with different second monomer unit of 4-hydroxybutyrate, 3-hydroxyhexanoate or 6-hydroxyhexanoate, were investigated by microbeam X-ray diffraction with Fresnel Zone Plate technique in synchrotron radiation (SPring-8). Radial scanning of spherulites were performed in 2 or 4 Pm steps with 0.5 mu m beam diameter of fine microfocus beam. The X-ray diffraction patterns for P(3HB) homopolymer spherulites showed the change of crystal orientation along the radial direction (a-axis), while the b- and c-axes rotated around a-axis. The intensities in microbeam X-ray diagrams of spherulites for P(3HB) copolymers changed periodically as function of the distance along the radial direction. The periodicity measured by X-ray diffraction was matched with narrow band spacing (15-25 mu m) observed by polarized optical microscopy. (c) 2005 Elsevier Ltd. All rights reserved.