Unique microphas© separation structures, different from bulk structure, are found in block-copolymer particles, which are considered three-dimensional confinement spaces. Block-copolymer particles were prepared by the self-organized precipitation (SORP) method. Electron microscopy revealed that the microphase separation structures in the particles changed from lamellae to various unique morphologies depending on the size of particles. © 2011 The Society of Polymer Science.