The superstructures of oxyethylene/oxybutylene block copolymers with different compositions and architectures (EmBn, BnEmBn and EmBnEm) were studied using polarized optical microscopy (POM). Several novel superstructures, such as fibril crystals and different frontiers of spherulites and crystallized regions, have been observed. It is found that the ability of forming spherulites is reduced with the decrease in the volume fraction of the crystallizable block. The unfavorable interaction between the blocks, which can be indicated by order-disorder transition temperature (T-ODT) also affects the formation of superstructure. The BnEmBn triblock copolymers exhibit the strongest ability of organization into spherulites, whereas the EmBnEm triblock copolymers show the weakest ability of organization into spherulites. (C) 2004 Elsevier Ltd. All rights reserved.